<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.3 20210610//EN" "https://jats.nlm.nih.gov/publishing/1.3/JATS-journalpublishing1-3.dtd"><article xml:lang="en" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" dtd-version="1.3" article-type="research-article"><front><journal-meta><journal-id journal-id-type="issn">2460-0245</journal-id><journal-title-group><journal-title>Journal of the Indonesian Mathematical Society</journal-title><abbrev-journal-title>JIMS</abbrev-journal-title></journal-title-group><issn pub-type="epub">2460-0245</issn><issn pub-type="ppub">2086-8952</issn><publisher><publisher-name>IndoMS</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.22342/jims.v32i1.1656</article-id><article-categories></article-categories><title-group><article-title>On K-AP And K-Avoid-AP Van Der Waerden Game</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Sim</surname><given-names>Kai An</given-names></name><address><country country="MY">Malaysia</country><email>kaians@sunway.edu.my</email></address><xref ref-type="aff" rid="AFF-1"></xref><xref ref-type="corresp" rid="cor-0"></xref></contrib><contrib contrib-type="author"><name><surname>Ruzali</surname><given-names>Wan Muhammad Afif Wan</given-names></name><address><country country="MY">Malaysia</country><email>wan.w126@imail.sunway.edu.my</email></address><xref ref-type="aff" rid="AFF-1"></xref></contrib><contrib contrib-type="author"><name><surname>Wong</surname><given-names>Kok Bin</given-names></name><address><country country="MY">Malaysia</country><email>kbwong@um.edu.my</email></address><xref ref-type="aff" rid="AFF-2"></xref></contrib><contrib contrib-type="author"><name><surname>Ho</surname><given-names>Chee Kit</given-names></name><address><country country="MY">Malaysia</country><email>ckho@sunway.edu.my</email></address><xref ref-type="aff" rid="AFF-1"></xref></contrib></contrib-group><contrib-group><contrib contrib-type="editor"><name><surname>Nurwigantara</surname><given-names>Mu'amar Musa</given-names></name><address><country country="ID">Indonesia</country><email>muamar.musa.n@mail.ugm.ac.id</email></address></contrib></contrib-group><aff id="AFF-1"><institution content-type="dept">School of Mathematical Sciences</institution><institution-wrap><institution>Sunway University</institution><institution-id institution-id-type="ror">https://ror.org/04mjt7f73</institution-id></institution-wrap><country country="MY">Malaysia</country></aff><aff id="AFF-2"><institution content-type="dept">Institute of Mathematical Sciences, Faculty of Science</institution><institution-wrap><institution>University of Malaya</institution><institution-id institution-id-type="ror">https://ror.org/00rzspn62</institution-id></institution-wrap><country country="MY">Malaysia</country></aff><author-notes><corresp id="cor-0">Corresponding author: Kai An Sim. Email: <email>kaians@sunway.edu.my</email></corresp></author-notes><pub-date date-type="pub" iso-8601-date="2026-03-01" publication-format="electronic"><day>01</day><month>03</month><year>2026</year></pub-date><pub-date date-type="collection" iso-8601-date="2026-01-05" publication-format="electronic"><day>05</day><month>01</month><year>2026</year></pub-date><volume>32</volume><issue>1</issue><issue-title>MARCH</issue-title><fpage>1</fpage><lpage>12</lpage><history><date date-type="received" iso-8601-date="2024-02-20"><day>20</day><month>02</month><year>2024</year></date><date date-type="accepted" iso-8601-date="2025-10-04"><day>04</day><month>10</month><year>2025</year></date></history><permissions><copyright-statement>Copyright (c) 2026 Journal of the Indonesian Mathematical Society</copyright-statement><copyright-year>2026</copyright-year><copyright-holder>Journal of the Indonesian Mathematical Society</copyright-holder><license license-type="open-access" xlink:href="https://creativecommons.org/licenses/by-nc-nd/4.0/"><ali:license_ref xmlns:ali="http://www.niso.org/schemas/ali/1.0/">https://creativecommons.org/licenses/by-nc-nd/4.0/</ali:license_ref><license-p>This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.</license-p></license></permissions><self-uri xlink:href="https://jims-a.org/index.php/jimsa/article/view/1656" xlink:title="1656"></self-uri><abstract><p>Let <italic>w</italic>(<italic>k</italic>; 2) be the van der Waerden number such that for every 2 colouring of [1, <italic>w</italic>(<italic>k</italic>; 2)] there is a monochromatic k-term arithmetic progression (AP). Consider the following two 2-players games: <italic>k</italic>-AP game and <italic>k</italic>-AVOID-AP game. These are two different games between two players, Player 1 and Player 2, on a sequence of integers [1, <italic>n</italic>] where n ∈ Z + . Each player's aim is to obtain or avoid forming a monochromatic k-term arithmetic progression. The player who first obtains a monochromatic k-term arithmetic progression wins or loses, thus ending the game. In this paper, we investigate these two games and propose a new parameter: the minimum number of turns ŵn(<italic>k</italic>) (and wn(<italic>k</italic>)) needed for any of the player to win in <italic>k</italic>-AP (and <italic>k</italic>-AVOID-AP game respectively). We propose the winning strategies for Player 1 and Player 2 and hence show that ŵn(3) = 5, ŵn(4) = 7 and wn(3) = 9. We also have shown that in a <italic>k</italic>-AVOID-AP game on [1, n], where <italic>n</italic> is sufficiently large, Player 2 always has a winning strategy if <italic>n</italic> is even.  </p></abstract><kwd-group><kwd>van der Waerden number</kwd><kwd>k-term arithmetic progression</kwd><kwd>k-AP game</kwd><kwd>k-AVOID-AP game</kwd></kwd-group><custom-meta-group><custom-meta><meta-name>File created by JATS Editor</meta-name><meta-value>https://jatseditor.com</meta-value></custom-meta><custom-meta><meta-name>issue-created-year</meta-name><meta-value>2026</meta-value></custom-meta></custom-meta-group></article-meta></front><body><sec id="sec-1"><title>1. Introduction</title><p>For an arithmetic progression <inline-formula><tex-math id="math-1"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle A = \left\{ a + l d : 0 \leq l \leq k - 1 \right\} \end{document} ]]></tex-math></inline-formula>, we say that <italic>A</italic> is a <italic>k-term arithmetic progression (AP) with diference d</italic>, or we write <inline-formula><tex-math id="math-2"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ a + l d \} _ { 0 \leq l \leq k - 1 } \end{document} ]]></tex-math></inline-formula> For a positive integer <italic>t</italic>, we denote the set <inline-formula><tex-math id="math-3"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ 1 , 2 , 3 , \ldots , t \} \end{document} ]]></tex-math></inline-formula> by <inline-formula><tex-math id="math-4"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, t] \end{document} ]]></tex-math></inline-formula>. An <italic>r-colouring</italic> of a set S is a surjective function <inline-formula><tex-math id="math-5"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \chi : S \rightarrow [1,r] \end{document} ]]></tex-math></inline-formula>. A <italic>monochromatic k-term arithmetic progression</italic> refers to a <italic>k</italic>-term arithmetic progression such that all of its elements are of the same colour. One of the most fundamental Ramsey-type theorem is the van der Waerden theorem. The van der Waerden’s theorem <xref ref-type="bibr" rid="BIBR-1">[1]</xref> states that there exists a least positive integer <inline-formula><tex-math id="math-6"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w = w ( k ; r ) \end{document} ]]></tex-math></inline-formula> such that for any n <inline-formula><tex-math id="math-7"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \geq w , \end{document} ]]></tex-math></inline-formula> , every <italic>r</italic>-colouring of [1, <italic>n</italic>] admits a monochromatic k-term arithmetic progression. For more results on van der Waerden numbers, see [<xref ref-type="bibr" rid="BIBR-2">2</xref>, <xref ref-type="bibr" rid="BIBR-3">3</xref>, <xref ref-type="bibr" rid="BIBR-4">4</xref>, <xref ref-type="bibr" rid="BIBR-5">5</xref>, <xref ref-type="bibr" rid="BIBR-6">6</xref>, <xref ref-type="bibr" rid="BIBR-7">7</xref>].<target id="anchor-56e56ed3-1b6c-4f31-8606-d5553bc25d11" target-type="reference-target"/></p><p><bold>Theorem 1.1.</bold><xref ref-type="bibr" rid="BIBR-1">[1]</xref><italic>(van der Waerden’s Theorem) Let </italic><inline-formula><tex-math id="math-8"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k , r \geq 2 \end{document} ]]></tex-math></inline-formula><italic> be integers. There exists a least positive integer </italic><inline-formula><tex-math id="math-9"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w = w ( k ; r ) \end{document} ]]></tex-math></inline-formula><italic> such that for any </italic><inline-formula><tex-math id="math-10"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq w , \end{document} ]]></tex-math></inline-formula><italic> every r-colouring of [1, n] admits a monochromatic k-term arithmetic progression.</italic></p><p>Note that exact values of <inline-formula><tex-math id="math-11"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula> are only known for small value of <italic>k</italic> where <inline-formula><tex-math id="math-12"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( 3 ; 2 ) = 9 , w ( 4 ; 2 ) = 3 5 , w ( 5 ; 2 ) = 1 7 8 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-13"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( 6 ; 2 ) = 1 1 3 2 \end{document} ]]></tex-math></inline-formula> , see <xref ref-type="bibr" rid="BIBR-5">[5]</xref>. The exact value of <inline-formula><tex-math id="math-14"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( k ; r ) \end{document} ]]></tex-math></inline-formula> is not known in general. We refer the readers to [<xref ref-type="bibr" rid="BIBR-4">4</xref>, <xref ref-type="bibr" rid="BIBR-3">3</xref>, <xref ref-type="bibr" rid="BIBR-8">8</xref>, <xref ref-type="bibr" rid="BIBR-9">9</xref>, <xref ref-type="bibr" rid="BIBR-6">6</xref>, <xref ref-type="bibr" rid="BIBR-7">7</xref>].</p><p>There are many variants of Ramsey games that have been investigated, see [<xref ref-type="bibr" rid="BIBR-10">10</xref>, <xref ref-type="bibr" rid="BIBR-11">11</xref>, <xref ref-type="bibr" rid="BIBR-12">12</xref>, <xref ref-type="bibr" rid="BIBR-13">13</xref>, <xref ref-type="bibr" rid="BIBR-14">14</xref>, <xref ref-type="bibr" rid="BIBR-15">15</xref>, <xref ref-type="bibr" rid="BIBR-16">16</xref>, <xref ref-type="bibr" rid="BIBR-17">17</xref>, <xref ref-type="bibr" rid="BIBR-18">18</xref>]. Consider one of the games here, which is inspired by Ramsey Theory: Player 1 (blue) and Player 2 (red) alternate colouring edges of a complete graph <inline-formula><tex-math id="math-15"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle K _ { m } \end{document} ]]></tex-math></inline-formula> with their colours. Let <inline-formula><tex-math id="math-16"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle H \end{document} ]]></tex-math></inline-formula> be a subgraph of <inline-formula><tex-math id="math-17"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle K _ { m } \end{document} ]]></tex-math></inline-formula>. The first player to avoid a monochromatic H in his colour wins. This motivates us to investigate a similar van der Waerden game as follows.</p><p>A <italic>k</italic>-AP van der Waerden game (or <italic>k</italic>-AP game) is a game between two players, Player 1 and Player 2, on the set of integers <inline-formula><tex-math id="math-18"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula>. Initially, all the integers <inline-formula><tex-math id="math-19"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 1 , 2 , \ldots , n \end{document} ]]></tex-math></inline-formula> are uncoloured. Player 1 will first select an integer and colour it with red. Player 2 will then select another integer and colour it with blue. The two players continue this alternating colouring process on uncoloured integers. Each player’s aim is to form a monochromatic <italic>k</italic>-term arithmetic progression as soon as possible. The player who first obtains a monochromatic <italic>k</italic>-term arithmetic progression wins, thus ending the game. We assume all players play optimally where both players never purposefully avoid a monochromatic <italic>k</italic>-term arithmetic progression and at the same time, they would like to prevent the opponent from forming a monochromatic k-term arithmetic progression.</p><p>A <italic>k</italic>-AVOID-AP van der Waerden game (or <italic>k</italic>-AVOID-AP game) is a game opposite to that of the <italic>k</italic>-AP van der waerden game where both players’ aims are to avoid forming a monochromatic k-term arithmetic progression. The player who first obtains a monochromatic k-term arithmetic progression loses, thus ending the game. We assume all players play optimally where both players never purposefully form a monochromatic k-term arithmetic progression and at the same time, they would like to “force” a monochromatic k-term arithmetic progression for the opponent.</p><p>We begin by explaining some notation. A <italic>turn</italic> of the game is an action of colouring by either Player 1 or Player 2. If they are playing on the set of integers [1, n] and <inline-formula><tex-math id="math-20"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula> , then by Theorem <xref ref-type="custom" custom-type="reference-target" rid="anchor-56e56ed3-1b6c-4f31-8606-d5553bc25d11">1.1</xref>, one of the players will win in <inline-formula><tex-math id="math-21"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k { \mathrm { - A P } } \end{document} ]]></tex-math></inline-formula> game when all the integers are coloured. Let <inline-formula><tex-math id="math-22"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { i } \end{document} ]]></tex-math></inline-formula> be the ith turn. Player 1 makes his move on the odd-numbered turns, whereas Player 2 makes his move on the even-numbered turns. Let <inline-formula><tex-math id="math-23"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { i } \end{document} ]]></tex-math></inline-formula> denote the status of the integer <italic>i</italic> where <inline-formula><tex-math id="math-24"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i \in [ 1 , n ] \end{document} ]]></tex-math></inline-formula> Specifically, <inline-formula><tex-math id="math-25"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { i } = 1 \end{document} ]]></tex-math></inline-formula> means that the number <italic>i</italic> has been coloured by Player 1 with red and <inline-formula><tex-math id="math-26"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { i } = 2 \end{document} ]]></tex-math></inline-formula> means that the number <italic>i</italic> has been coloured by Player 2 with blue. A player is said to have a winning strategy if he will win the game by choosing certain integers at each of his turn regardless of what integer the other player chooses at the other player’s turn.</p><p>In a <inline-formula><tex-math id="math-27"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k { \mathrm { - A P } } \end{document} ]]></tex-math></inline-formula> game on the set of integers <inline-formula><tex-math id="math-28"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula> , let <inline-formula><tex-math id="math-29"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> to be the minimum number of turns for any of the players to win the game (i.e. the minimum number of turns to form a <italic>k</italic>-term arithmetic progression). This means that if <inline-formula><tex-math id="math-30"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> is odd, then Player 1 wins and if <inline-formula><tex-math id="math-31"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> is even, then Player 2 wins. In a <inline-formula><tex-math id="math-32"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k { \mathrm { - A V O I D - A P } } \end{document} ]]></tex-math></inline-formula> game on the set of integers <inline-formula><tex-math id="math-33"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula> , let <inline-formula><tex-math id="math-34"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> to be the minimum number of turns for any of the players to win the game (i.e. the minimum number of turns for the opponent to form a <italic>k</italic>-term arithmetic progression). So, if <inline-formula><tex-math id="math-35"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> is odd, then Player 1 loses and if <inline-formula><tex-math id="math-36"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> is even, then Player 2 loses. Clearly, if <inline-formula><tex-math id="math-37"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n = w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula> , then <inline-formula><tex-math id="math-38"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle { \hat { w } } _ { n } ( k ) \leq w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-39"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \leq w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula></p></sec><sec id="sec-2"><title>2. k-term arithmetic progression in a k-AP game</title><p>In a <italic>k</italic>-AP game, there are three possibilities:</p><list list-type="order"><list-item><p>Player 1 has a winning strategy.</p></list-item><list-item><p>Player 2 has a winning strategy.</p></list-item><list-item><p>Both players have no winning strategy.</p></list-item></list><p>First, we show that only (1) and (3) are possible.</p><p><bold>Theorem 2.1.</bold><italic>In a k-AP game on the set of integers </italic><inline-formula><tex-math id="math-40"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula><italic> , either Player 1 has a winning strategy or both players have no winning strategy.</italic></p><p><italic>Proof.</italic> Suppose Player 2 has a winning strategy <inline-formula><tex-math id="math-41"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } \end{document} ]]></tex-math></inline-formula> on <inline-formula><tex-math id="math-42"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula>. At <inline-formula><tex-math id="math-43"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 1 with red. By using the strategy <inline-formula><tex-math id="math-44"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } \end{document} ]]></tex-math></inline-formula>, Player 2 will need to colour <inline-formula><tex-math id="math-45"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \in [ 2 , n ] \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-46"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> with blue. Now, Player 1 shall assume that he had not coloured 1 with red at <inline-formula><tex-math id="math-47"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } \end{document} ]]></tex-math></inline-formula>, and Player 2 has coloured <inline-formula><tex-math id="math-48"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \end{document} ]]></tex-math></inline-formula> at turn <inline-formula><tex-math id="math-49"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> with blue. Basically, Player 1 assume himself as the second player and assume Player 2 as the first player. Using the strategy <inline-formula><tex-math id="math-50"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } \end{document} ]]></tex-math></inline-formula>, Player 1 will need to colour <inline-formula><tex-math id="math-51"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } \in [ 1 , n ] \backslash \{ b _ { 1 } \} \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-52"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> with red. If <inline-formula><tex-math id="math-53"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } = 1 \end{document} ]]></tex-math></inline-formula>， then Player 1 simply chooses another uncoloured integer, say <inline-formula><tex-math id="math-54"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> , and colours it with red. If <inline-formula><tex-math id="math-55"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } \neq 1 \end{document} ]]></tex-math></inline-formula> , then Player 1 will colour <inline-formula><tex-math id="math-56"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } \end{document} ]]></tex-math></inline-formula> with red.</p><p>At <inline-formula><tex-math id="math-57"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours <inline-formula><tex-math id="math-58"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 2 } \in [ 2 , n ] \ \backslash \ \{ a _ { 1 } \} \end{document} ]]></tex-math></inline-formula> with blue according to the strategy <inline-formula><tex-math id="math-59"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } . \mathrm { \ A t \ } T _ { 4 } ^ { \prime } , \end{document} ]]></tex-math></inline-formula> , Player 1 will need to colour <inline-formula><tex-math id="math-60"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } \in [ 1 , n ] \backslash \{ b _ { 1 } , a _ { 1 } , b _ { 2 } \} \end{document} ]]></tex-math></inline-formula> with red. We consider two cases:</p><p><bold>Case 1:</bold> Suppose <inline-formula><tex-math id="math-61"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } \neq 1 \end{document} ]]></tex-math></inline-formula>. If <inline-formula><tex-math id="math-62"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } = 1 \end{document} ]]></tex-math></inline-formula> , then Player 1 simply choose another uncoloured integer, say <inline-formula><tex-math id="math-63"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> and colour it with red. If <inline-formula><tex-math id="math-64"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } \neq 1 \end{document} ]]></tex-math></inline-formula> , then Player 1 will colour <inline-formula><tex-math id="math-65"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } \end{document} ]]></tex-math></inline-formula> with red.</p><p><bold>Case 2:</bold> Suppose <inline-formula><tex-math id="math-66"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } = 1 \end{document} ]]></tex-math></inline-formula>. Then both <inline-formula><tex-math id="math-67"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> and 1 are already coloured by red. In this scenario, if <inline-formula><tex-math id="math-68"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } = a _ { 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> , then Player 1 simply choose another uncoloured integer, say <inline-formula><tex-math id="math-69"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 3 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> and colour it with red. If <inline-formula><tex-math id="math-70"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } \neq a _ { 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> , then Player 1 will colour <inline-formula><tex-math id="math-71"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 2 } \end{document} ]]></tex-math></inline-formula> with red. The two players will continue this process until one of them wins.</p><p>Since Player 2 is using the strategy <inline-formula><tex-math id="math-72"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } \end{document} ]]></tex-math></inline-formula> , at <inline-formula><tex-math id="math-73"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 m } \end{document} ]]></tex-math></inline-formula> , Player 2 would have coloured <italic>m</italic> distinct integers <inline-formula><tex-math id="math-74"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } , b _ { 2 } , \dots , b _ { m } \end{document} ]]></tex-math></inline-formula> and there is a <italic>k</italic>-term arithmetic progression among them. At <inline-formula><tex-math id="math-75"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 m - 1 } \end{document} ]]></tex-math></inline-formula> , Player 1 have coloured m distinct integers <inline-formula><tex-math id="math-76"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 1 , a _ { 1 } , a _ { 2 } , \dotsc , a _ { m - 1 } \end{document} ]]></tex-math></inline-formula> Note that there should not be any k-term arithmetic progressions in <inline-formula><tex-math id="math-77"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ 1 , a _ { 1 } , b _ { 2 } \end{document} ]]></tex-math></inline-formula><inline-formula><tex-math id="math-78"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \dots , a _ { m - 1 } \big \} \end{document} ]]></tex-math></inline-formula></p><p>On the other hand, Player 1 is using the same strategy <inline-formula><tex-math id="math-79"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta _ { n } \end{document} ]]></tex-math></inline-formula> to win. <inline-formula><tex-math id="math-80"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle { \mathrm { S o } } , \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-81"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 m - 2 } ^ { \prime } , \end{document} ]]></tex-math></inline-formula> Player 1 have coloured <inline-formula><tex-math id="math-82"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle m - 1 \end{document} ]]></tex-math></inline-formula> distinct integers <inline-formula><tex-math id="math-83"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { 1 } , a _ { 2 } , \dots , a _ { m - 1 } \end{document} ]]></tex-math></inline-formula>. Since there is no k-term arithmetic progressions in <inline-formula><tex-math id="math-84"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ a _ { 1 } , a _ { 2 } , \dotsc , a _ { m - 1 } \} \end{document} ]]></tex-math></inline-formula> , at <inline-formula><tex-math id="math-85"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 m - 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> , Player 2 could not have won. But at <inline-formula><tex-math id="math-86"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 m - 1 } ^ { \prime } \end{document} ]]></tex-math></inline-formula> , Player 2 have coloured m distinct integers <inline-formula><tex-math id="math-87"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } , b _ { 2 } , \dots , b _ { m } \end{document} ]]></tex-math></inline-formula> and there is a <italic>k</italic>-term arithmetic progression in <inline-formula><tex-math id="math-88"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ b _ { 1 } , b _ { 2 } , \dots , b _ { m } \} \end{document} ]]></tex-math></inline-formula> , a contradiction. Hence, Player 2 does not have a winning strategy and the theorem follows. □</p><p>We will show that in a <italic>k</italic>-AP game where <inline-formula><tex-math id="math-89"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k = 3 , 4 \end{document} ]]></tex-math></inline-formula> , Player 1 will have a winning strategy. Furthermore, we show that <inline-formula><tex-math id="math-90"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 3 ) = 5 \end{document} ]]></tex-math></inline-formula> in  <inline-formula><tex-math id="math-91"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula>where <inline-formula><tex-math id="math-92"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n = w ( k ; 2 ) = 9 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-93"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 4 ) = 7 \end{document} ]]></tex-math></inline-formula> in <inline-formula><tex-math id="math-94"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula> where <inline-formula><tex-math id="math-95"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n = 2 5 < w ( 4 ; 2 ) = 3 5 \end{document} ]]></tex-math></inline-formula><target id="anchor-cd5439d3-e124-4937-8a89-88039e2d0689" target-type="reference-target"/></p><p><bold>Lemma 2.2.</bold><italic>In a k-AP game on the set of integers </italic><inline-formula><tex-math id="math-96"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] , { \hat { w } } _ { n } ( k ) \geq 2 k - 1 \end{document} ]]></tex-math></inline-formula></p><p><italic>Proof.</italic> In order to form a monochromatic <italic>k</italic>-term arithmetic progression in <inline-formula><tex-math id="math-97"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula> the winner has to choose at least <italic>k</italic> integers. If Player 2 wins the game, then Player 1 must have chosen at least <italic>k</italic> integers; hence <inline-formula><tex-math id="math-98"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \ge k + k = 2 k \end{document} ]]></tex-math></inline-formula> . If Player 1 wins the game, then Player 2 has to choose <inline-formula><tex-math id="math-99"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k - 1 \end{document} ]]></tex-math></inline-formula> integers and hence <inline-formula><tex-math id="math-100"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \geq k + k - 1 = 2 k - 1 \end{document} ]]></tex-math></inline-formula>. The result follows. □<target id="anchor-baba779b-43bd-4696-9134-e015f8825fb7" target-type="reference-target"/></p><p><bold>Lemma 2.3.</bold><italic>Suppose there is a sequence of increasing integers</italic></p><disp-formula id="equation-1"><tex-math id="math-101"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c c c c} t _ {0} & t _ {1} & t _ {2} & \underline {{t _ {3}}} & t _ {4} & \underline {{t _ {5}}} & t _ {6} & \underline {{t _ {7}}} & t _ {8}, \end{array} \end{document} ]]></tex-math></disp-formula><p>where <inline-formula><tex-math id="math-102"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { i + 1 } - t _ { i } = t _ { j + 1 } - t _ { j } \end{document} ]]></tex-math></inline-formula> for all <inline-formula><tex-math id="math-103"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i , j \end{document} ]]></tex-math></inline-formula> . If at turn <inline-formula><tex-math id="math-104"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i } \end{document} ]]></tex-math></inline-formula> (Player 2’s turn), <inline-formula><tex-math id="math-105"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 4 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-106"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 6 } \end{document} ]]></tex-math></inline-formula> have been coloured with red and <inline-formula><tex-math id="math-107"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { i } \end{document} ]]></tex-math></inline-formula> has not been coloured for all <inline-formula><tex-math id="math-108"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i \not \in \{ 1 , 4 , 6 \} \end{document} ]]></tex-math></inline-formula> , then regardless of Player <inline-formula><tex-math id="math-109"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle { \mathit { 2 3 } } \end{document} ]]></tex-math></inline-formula> choices at <inline-formula><tex-math id="math-110"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i } \end{document} ]]></tex-math></inline-formula> or <inline-formula><tex-math id="math-111"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 2 } \end{document} ]]></tex-math></inline-formula> , Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-112"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 3 } \end{document} ]]></tex-math></inline-formula>.</p><p><italic>Proof.</italic> Assume that at <inline-formula><tex-math id="math-113"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i } \end{document} ]]></tex-math></inline-formula>, Player 2 colours <inline-formula><tex-math id="math-114"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { i } \end{document} ]]></tex-math></inline-formula> with blue. Suppose <inline-formula><tex-math id="math-115"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { i } \in \{ t _ { 3 } , t _ { 5 } , t _ { 7 } \} \end{document} ]]></tex-math></inline-formula> Then at <inline-formula><tex-math id="math-116"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 1 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours <inline-formula><tex-math id="math-117"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 2 } \end{document} ]]></tex-math></inline-formula> with red. Now, <inline-formula><tex-math id="math-118"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 0 } , t _ { 2 } , t _ { 4 } , t _ { 6 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-119"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 2 } , t _ { 4 } , t _ { 6 } , t _ { 8 } \end{document} ]]></tex-math></inline-formula> are two 4-term arithmetic progressions and all of these integers are coloured with red except <inline-formula><tex-math id="math-120"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 0 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-121"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 8 } \end{document} ]]></tex-math></inline-formula> , which are not coloured. So, regardless of any choice Player 2 makes at <inline-formula><tex-math id="math-122"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 2 } \end{document} ]]></tex-math></inline-formula> , Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-123"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 3 } \end{document} ]]></tex-math></inline-formula> by colouring t or <inline-formula><tex-math id="math-124"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 8 } \end{document} ]]></tex-math></inline-formula> with red.</p><p>Suppose <inline-formula><tex-math id="math-125"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { i } \notin \{ t _ { 3 } , t _ { 5 } , t _ { 7 } \} \end{document} ]]></tex-math></inline-formula>. Then at <inline-formula><tex-math id="math-126"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 1 } \end{document} ]]></tex-math></inline-formula>, Player 1 colours <inline-formula><tex-math id="math-127"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 5 } \end{document} ]]></tex-math></inline-formula> with red. Now, <inline-formula><tex-math id="math-128"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 3 } , t _ { 4 } , t _ { 5 } , t _ { 6 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-129"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 4 } , t _ { 5 } , t _ { 6 } , t _ { 7 } \end{document} ]]></tex-math></inline-formula> are two 4-term arithmetic progressions and all of these integers are coloured with red except <inline-formula><tex-math id="math-130"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 3 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-131"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 7 } \end{document} ]]></tex-math></inline-formula> , which are not coloured. So, regardless of any choice Player <inline-formula><tex-math id="math-132"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 2 \end{document} ]]></tex-math></inline-formula> makes at <inline-formula><tex-math id="math-133"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 2 } \end{document} ]]></tex-math></inline-formula> , Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-134"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 i + 3 } \end{document} ]]></tex-math></inline-formula> by colouring <inline-formula><tex-math id="math-135"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 3 } \end{document} ]]></tex-math></inline-formula> or <inline-formula><tex-math id="math-136"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle t _ { 7 } \end{document} ]]></tex-math></inline-formula> with red. □</p><p><bold>Theorem 2.4.</bold><italic>Consider a k-AP game on </italic><inline-formula><tex-math id="math-137"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula></p><list list-type="order"><list-item><p>If <inline-formula><tex-math id="math-138"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k = 3 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-139"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq 5 \end{document} ]]></tex-math></inline-formula> , then Player 1 has a winning strategy. Furthermore, <inline-formula><tex-math id="math-140"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 3 ) = 5 \end{document} ]]></tex-math></inline-formula>.</p></list-item><list-item><p>If <inline-formula><tex-math id="math-141"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k = 4 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-142"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq 2 5 \end{document} ]]></tex-math></inline-formula> , then Player 1 has a winning strategy. Furthermore, <inline-formula><tex-math id="math-143"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 4 ) = 7 \end{document} ]]></tex-math></inline-formula>.</p></list-item></list><p><italic>Proof.</italic> (a) By Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-cd5439d3-e124-4937-8a89-88039e2d0689">2.2</xref>, it is clear that <inline-formula><tex-math id="math-144"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 3 ) \geq 5 . \mathrm { ~ A t ~ } T _ { 1 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 3 with red. Suppose Player 2 colours 1 with blue <inline-formula><tex-math id="math-145"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> . At T3, Player 1 colours 4 with red. A 3-term arithmetic progression with red colour is formed if 2 or 5 is coloured by Player 1 at <inline-formula><tex-math id="math-146"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } . \ \mathrm { S o } , \end{document} ]]></tex-math></inline-formula> regardless of which integer is coloured by Player 2 at <inline-formula><tex-math id="math-147"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , Player 1 will win.</p><p>Suppose Player 2 colours 2 with blue at <inline-formula><tex-math id="math-148"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> . At <inline-formula><tex-math id="math-149"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 5 with red. A 3-term arithmetic progression with red colour is formed if 1 or 4 is coloured by Player 1 at <inline-formula><tex-math id="math-150"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula>. So, regardless of which integer is coloured by Player 2 at <inline-formula><tex-math id="math-151"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> Player 1 will also win.</p><p>Suppose Player 2 colours an integer <inline-formula><tex-math id="math-152"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a \ge 4 \end{document} ]]></tex-math></inline-formula> with blue at <inline-formula><tex-math id="math-153"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula>. Player 1 colours 1 with red if <inline-formula><tex-math id="math-154"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a = 4 \end{document} ]]></tex-math></inline-formula> and colours 2 with red if <inline-formula><tex-math id="math-155"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a \neq 4 \end{document} ]]></tex-math></inline-formula>. In either case, it is not hard to see that Player 1 will win at <inline-formula><tex-math id="math-156"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> regardless of any choice Player 2 makes at <inline-formula><tex-math id="math-157"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula>.</p><p>(b) By Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-cd5439d3-e124-4937-8a89-88039e2d0689">2.2</xref>, it is clear that <inline-formula><tex-math id="math-158"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 4 ) \ge 7 \end{document} ]]></tex-math></inline-formula> . To show that the equality holds, we shall show that Player 1 has a winning strategy and will win at <inline-formula><tex-math id="math-159"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> , regardless of the choices made by Player <inline-formula><tex-math id="math-160"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 2 \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-161"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } , T _ { 4 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-162"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . At <inline-formula><tex-math id="math-163"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } \end{document} ]]></tex-math></inline-formula>, Player 1 colours 13 with red. <inline-formula><tex-math id="math-164"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \mathrm { A t } ~ T _ { 2 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours <inline-formula><tex-math id="math-165"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \end{document} ]]></tex-math></inline-formula> with blue. Now, we look at the following two diferent sequences:</p><disp-formula id="equation-2"><tex-math id="math-166"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c c c} 1 & 7 & \underline {{1 0}} & 1 3 & \underline {{1 6}} & 1 9 & \underline {{2 2}} & 2 5 \\ 5 & 9 & \underline {{1 1}} & 1 3 & \underline {{1 5}} & 1 7 & \underline {{1 9}} & 2 1. \end{array} \end{document} ]]></tex-math></disp-formula><p>Suppose <inline-formula><tex-math id="math-167"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \in \{ 1 , 7 , 1 0 , 1 6 , 2 2 , 2 5 \} \end{document} ]]></tex-math></inline-formula> . Then <inline-formula><tex-math id="math-168"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \notin \{ 5 , 9 , 1 1 , 1 5 , 1 7 , 1 9 , 2 1 \} \end{document} ]]></tex-math></inline-formula> . At <inline-formula><tex-math id="math-169"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 17 with red. At <inline-formula><tex-math id="math-170"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , in the following sequence of integers</p><disp-formula id="equation-3"><tex-math id="math-171"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c c c c} 5 & 7 & 9 & \underline {{1 1}} & 1 3 & \underline {{1 5}} & 1 7 & \underline {{1 9}} & 2 1, \end{array} \end{document} ]]></tex-math></disp-formula><p>we see that integers 13 and 17 are coloured with red and the integers 5, 9, 11, 15, 19, 21 are not coloured. <inline-formula><tex-math id="math-172"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \mathrm { B y } \end{document} ]]></tex-math></inline-formula> Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-baba779b-43bd-4696-9134-e015f8825fb7">2.3</xref>, Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-173"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula>.</p><p>Suppose <inline-formula><tex-math id="math-174"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } = 1 9 \end{document} ]]></tex-math></inline-formula>. Then at <inline-formula><tex-math id="math-175"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 9 with red. At <inline-formula><tex-math id="math-176"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula>, in the following sequence of integers</p><disp-formula id="equation-4"><tex-math id="math-177"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c c c c} 1 & 3 & 5 & \underline {{7}} & 9 & \underline {{1 1}} & 1 3 & \underline {{1 5}} & 1 7, \end{array} \end{document} ]]></tex-math></disp-formula><p>we see that integers 9 and 13 are coloured with red and the integers 1, 5, 7, 11, 15, 17 are not coloured. By Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-baba779b-43bd-4696-9134-e015f8825fb7">2.3</xref>, Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-178"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula>.</p><p>Suppose <inline-formula><tex-math id="math-179"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle b _ { 1 } \notin \{ 1 , 7 , 1 0 , 1 6 , 1 9 , 2 2 , 2 5 \} \end{document} ]]></tex-math></inline-formula> . Then at <inline-formula><tex-math id="math-180"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 19 with red. At <inline-formula><tex-math id="math-181"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , in the following sequence of integers</p><disp-formula id="equation-5"><tex-math id="math-182"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c c c c} 1 & 4 & 7 & \underline {{1 0}} & 1 3 & \underline {{1 6}} & 1 9 & \underline {{2 2}} & 2 5, \end{array} \end{document} ]]></tex-math></disp-formula><p>we see that integers 13 and 19 are coloured with red and the integers 1, 7, 10, 16, 22, 25 are not coloured. By Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-baba779b-43bd-4696-9134-e015f8825fb7">2.3</xref>, Player 1 will obtain a 4-term arithmetic progression with red at <inline-formula><tex-math id="math-183"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula>.</p><p>To better describe Player 1’s strategy, we use the following graph for better ilustrations.</p><fig id="figure-1"><label>Figure 1</label><graphic xlink:href="https://jims-a.org/index.php/jimsa/article/download/1656/546/13885" mime-subtype="jpeg" mimetype="image"><alt-text>Figure 1</alt-text></graphic></fig></sec><sec id="sec-3"><title>3. k-term arithmetic progression in k-AVOID-AP game</title><p>In this section, we shall consider <italic>k</italic>-AVOID-AP games.<target id="anchor-8924c5c8-dba6-475f-93d0-d99e9cb303f5" target-type="reference-target"/></p><p><bold>Theorem 3.1.</bold><italic>Let </italic><inline-formula><tex-math id="math-184"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula><italic> and set </italic><inline-formula><tex-math id="math-185"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle N = n \ i f n \end{document} ]]></tex-math></inline-formula><italic> is even, otherwise set </italic><inline-formula><tex-math id="math-186"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle N = n { + } 1 \end{document} ]]></tex-math></inline-formula><italic> Then, in a k-AVOID-AP game on </italic><inline-formula><tex-math id="math-187"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , N ] \end{document} ]]></tex-math></inline-formula><italic> , Player 2 always has a winning strategy.</italic></p><p><italic>Proof.</italic> Note that <italic>N</italic> is always even. We can illustrate the interval <inline-formula><tex-math id="math-188"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , N ] \end{document} ]]></tex-math></inline-formula> as an array below:</p><disp-formula id="equation-6"><tex-math id="math-189"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 1 \quad 2 \quad 3 \quad \dots \quad \frac {N}{2} - 1 \quad \frac {N}{2}\tag{1} \end{document} ]]></tex-math></disp-formula><disp-formula id="equation-7"><tex-math id="math-190"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \begin{array}{c c c c c c} N & N - 1 & N - 2 & \ldots & \frac {N}{2} + 2 & \frac {N}{2} + 1 \end{array} \end{document} ]]></tex-math></disp-formula><p>Consider any turn <inline-formula><tex-math id="math-191"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { i } \end{document} ]]></tex-math></inline-formula> where i is odd. If Player 1 chooses an integer <inline-formula><tex-math id="math-192"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle a _ { i } \in [ 1 , N ] \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-193"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { i } \end{document} ]]></tex-math></inline-formula>, then Player 2 is able to choose the integer <inline-formula><tex-math id="math-194"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle N - a _ { i } + 1 \end{document} ]]></tex-math></inline-formula> on the following turn <inline-formula><tex-math id="math-195"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { i + 1 } \end{document} ]]></tex-math></inline-formula> . Referring to our array (1) above, this means that Player 2 is choosing the integer that is mirrored by the separation between the first and second rows. For example, if Player 1 chooses 3, then Player 2 chooses <inline-formula><tex-math id="math-196"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle N - 2 \end{document} ]]></tex-math></inline-formula> , which is directly below 3 in array (1). The same is true if Player 1 chooses a number in the second row of the array; Player 2 will choose the number directly above it. Hence, Player 2 will always have an available ‘mirrored’ number to choose from after Player 1’s turns. As long as Player 1 does not obtain a <italic>k</italic>-term arithmetic progression, Player 2 will also not obtain a <italic>k</italic>-term arithmetic progression. By van der Waerden’s theorem, because <inline-formula><tex-math id="math-197"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle N \ge n \ge w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula>, an arithmetic progression will eventually be formed. Since Player 1 always makes his colouring choices a turn earlier, Player 1 will obtain a monochromatic <italic>k</italic>-term arithmetic progression before Player 2 does, thus losing the game. Hence, Player 2 will always win. □</p><p><bold>Corollary 3.2.</bold><italic>In a k-AVOID-AP game on [1, n], if </italic><inline-formula><tex-math id="math-198"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n \geq w ( k ; 2 ) \end{document} ]]></tex-math></inline-formula><italic> and n is even, then </italic><inline-formula><tex-math id="math-199"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \leq n - 1 \end{document} ]]></tex-math></inline-formula><bold><italic>.</italic></bold></p><p><italic>Proof.</italic> By Theorem <xref ref-type="custom" custom-type="reference-target" rid="anchor-8924c5c8-dba6-475f-93d0-d99e9cb303f5">3.1</xref>, if <italic>n</italic> is even, then it is clear that Player 2 will win. Furthermore, even with an optimum strategy used by Player 1, Player 2 may keep avoiding a monochromatic <italic>k</italic>-term arithmetic progression in his colour until his second last turn. Hence Player 1 will form a <italic>k</italic>-term arithmetic progression in his colour in his last turn before Player 2 chooses the last integer. Hence, <inline-formula><tex-math id="math-200"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \leq n - 1 \end{document} ]]></tex-math></inline-formula> .□</p><p><bold>Lemma 3.3.</bold><italic>If Player 2 has a strategy to avoid k-term arithmetic progressions on [1, n], then Player 1 has a strategy to avoid </italic><inline-formula><tex-math id="math-201"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( k + 1 ) \end{document} ]]></tex-math></inline-formula><italic>-term arithmetic progressions on </italic><inline-formula><tex-math id="math-202"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n + 1 ] \end{document} ]]></tex-math></inline-formula><italic> . Hence, </italic><inline-formula><tex-math id="math-203"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n + 1 } ( k + 1 ) \leq \tilde { w } _ { n } ( k ) + 1 \end{document} ]]></tex-math></inline-formula><italic>.</italic></p><p><italic>Proof.</italic> Suppose Player 2 has a strategy <inline-formula><tex-math id="math-204"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta \end{document} ]]></tex-math></inline-formula> to avoid <italic>k</italic>-term arithmetic progressions on <inline-formula><tex-math id="math-205"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n ] \end{document} ]]></tex-math></inline-formula> . Then, in <inline-formula><tex-math id="math-206"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1 , n + 1 ] \end{document} ]]></tex-math></inline-formula> , Player 1 colours integer <inline-formula><tex-math id="math-207"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n + 1 \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-208"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } \end{document} ]]></tex-math></inline-formula> with red, then in the rest of his turns, Player 1 can use strategy <inline-formula><tex-math id="math-209"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \delta \end{document} ]]></tex-math></inline-formula> to avoid monochromatic <italic>k</italic>-term arithmetic progressions on <inline-formula><tex-math id="math-210"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula>. As a result, Player 1 may avoid <inline-formula><tex-math id="math-211"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k + 1 \end{document} ]]></tex-math></inline-formula>-term arithmetic progressions in the game even with the integer <inline-formula><tex-math id="math-212"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n { \mathrel { + { 1 } } } \end{document} ]]></tex-math></inline-formula> coloured by him. □</p><p>In the next subsection, we will show that when <inline-formula><tex-math id="math-213"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle n = w ( 3 ; 2 ) = 9 \end{document} ]]></tex-math></inline-formula> , Player 2 still wins (Corollary <xref ref-type="custom" custom-type="reference-target" rid="anchor-fe254d85-d0d9-4d5b-b32c-67c1305a93e5">3.7</xref>).</p><sec id="sec-4"><title>3.1. 3-AVOID-AP game on [1, 9]</title><p><target id="anchor-3184727f-fc1b-4620-8134-da95d74aa10f" target-type="reference-target"/></p><p><bold>Lemma 3.4.</bold><italic>In a 3-AVOID-AP game on </italic>[1, 9]<italic>, Player 1 has a strategy to avoid defeat (or avoid forming a monochromatic 3-term arithmetic progression) until </italic><inline-formula><tex-math id="math-214"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula><italic>.</italic></p><p><italic>Proof.</italic> Let <inline-formula><tex-math id="math-215"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { i } = \{ 2 i - 1 , 2 i \} \end{document} ]]></tex-math></inline-formula> for <inline-formula><tex-math id="math-216"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i = { 1 , 2 , 3 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-217"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { 4 } = \{ 7 , 8 , 9 \} \end{document} ]]></tex-math></inline-formula> . At <inline-formula><tex-math id="math-218"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 1 } \end{document} ]]></tex-math></inline-formula> , Player 1 will colour 8 with red. If Player 2 colours 9 with blue at <inline-formula><tex-math id="math-219"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> , then Player 1 colours 7 with red at <inline-formula><tex-math id="math-220"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> . If Player 2 did not colour 9 at <inline-formula><tex-math id="math-221"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> , then Player 1 will colour 9 with red at <inline-formula><tex-math id="math-222"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> . Hence, after <inline-formula><tex-math id="math-223"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 3 } \end{document} ]]></tex-math></inline-formula> , we have the following two cases.</p><p><bold>Case 1.</bold><inline-formula><tex-math id="math-224"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( I _ { 7 } , I _ { 8 } , I _ { 9 } ) = ( 1 , 1 , 2 ) \end{document} ]]></tex-math></inline-formula>. Player 2 colours an integer at <inline-formula><tex-math id="math-225"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula>. By the pigeonhole principle, at <inline-formula><tex-math id="math-226"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , we let Player 1 colour 1, or otherwise colour 2 if 1 has been coloured by Player 2. If Player 1 colours 1 at <inline-formula><tex-math id="math-227"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then at <inline-formula><tex-math id="math-228"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> , Player 1 can colour 2, 3 or 5. Any of these choices will not form a red monochromatic 3-term arithmetic progression. If Player 1 colours <inline-formula><tex-math id="math-229"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 2 \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-230"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then after <inline-formula><tex-math id="math-231"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , ( I _ { 1 } , I _ { 2 } , I _ { 7 } , I _ { 8 } , I _ { 9 } ) = ( 2 , 1 , 1 , 1 , 2 ) \end{document} ]]></tex-math></inline-formula> . Hence,</p><p>Player 1 can colour 3 or 4 at <inline-formula><tex-math id="math-232"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> without forming a red monochromatic 3-term arithmetic progression.</p><p><bold>Case 2.</bold><inline-formula><tex-math id="math-233"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( I _ { 8 } , I _ { 9 } ) = ( 1 , 1 ) \end{document} ]]></tex-math></inline-formula>. Suppose at <inline-formula><tex-math id="math-234"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 2 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-235"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours integers in <inline-formula><tex-math id="math-236"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { i } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-237"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { j } \end{document} ]]></tex-math></inline-formula> respectively (<italic>i</italic> may be equal to <italic>j)</italic> . After <inline-formula><tex-math id="math-238"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula>, integers in <inline-formula><tex-math id="math-239"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { k } \end{document} ]]></tex-math></inline-formula> are not coloured for some <inline-formula><tex-math id="math-240"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k = 1 \end{document} ]]></tex-math></inline-formula>or <inline-formula><tex-math id="math-241"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 2 \end{document} ]]></tex-math></inline-formula> . At <inline-formula><tex-math id="math-242"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours an uncoloured integer in <inline-formula><tex-math id="math-243"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { k } \end{document} ]]></tex-math></inline-formula> with red. Now, <inline-formula><tex-math id="math-244"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { k } \end{document} ]]></tex-math></inline-formula> has two integers and one of them is coloured with red by Player 1 at <inline-formula><tex-math id="math-245"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> . If the other integer has not been coloured by Player 2 at <inline-formula><tex-math id="math-246"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>, then Player 1 colours the uncoloured integer in <inline-formula><tex-math id="math-247"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { k } \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-248"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula>. We are done. If Player 2 colours the integer in <inline-formula><tex-math id="math-249"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { k } \end{document} ]]></tex-math></inline-formula> with blue at <inline-formula><tex-math id="math-250"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } , \end{document} ]]></tex-math></inline-formula> then at <inline-formula><tex-math id="math-251"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> , Player 1 colours 5 or 6 (in which case does not result in a red monochromatic 3-term arithmetic progression) if both of these integers are uncoloured yet, or else colours any other uncoloured integers in <inline-formula><tex-math id="math-252"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { 1 } \end{document} ]]></tex-math></inline-formula> or <inline-formula><tex-math id="math-253"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle C _ { 2 } \end{document} ]]></tex-math></inline-formula>.</p><p>For all cases, Player 1 does not form a monochromatic 3-term arithmetic progression until <inline-formula><tex-math id="math-254"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> . This completes the proof. □</p><p>Before we move to the next result, we introduce the parameter <inline-formula><tex-math id="math-255"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \end{document} ]]></tex-math></inline-formula> which refers to the number of possible moves available to Player 2 to avoid a monochromatic 3-term arithmetic progression after <inline-formula><tex-math id="math-256"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>. Below we give an example:</p><disp-formula id="equation-8"><tex-math id="math-257"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \texttt {2 1 1 \_ \_ 2 \_ 1 2} \end{document} ]]></tex-math></disp-formula><p>The above represents the state of <inline-formula><tex-math id="math-258"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \mathrm { a \ 3 { - } A V O I D { - } A P } \end{document} ]]></tex-math></inline-formula> game on <inline-formula><tex-math id="math-259"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [ 1, 9] \end{document} ]]></tex-math></inline-formula>, after Player 2 colours a number during <inline-formula><tex-math id="math-260"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>. Instead of writing the numbers <inline-formula><tex-math id="math-261"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 1 , \ldots , 9 \end{document} ]]></tex-math></inline-formula> for the interval, we instead represent the coloured numbers with the numbers 1 and 2 to represent each Players’ choices so far, and the uncoloured numbers are left as blank spaces. The above represents the state whereI  <inline-formula><tex-math id="math-262"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle _ { 2 } = I _ { 3 } = I _ { 8 } = 1 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-263"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 1 } = I _ { 6 } = I _ { 9 } = 2 \end{document} ]]></tex-math></inline-formula>. From here, we see that Player 2 has two winning moves for the upcoming <inline-formula><tex-math id="math-264"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula>, by colouring either 4 or 7. In other words, either <inline-formula><tex-math id="math-265"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 4 } = 2 \end{document} ]]></tex-math></inline-formula> or<inline-formula><tex-math id="math-266"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 7 } = 2 \end{document} ]]></tex-math></inline-formula> at  <inline-formula><tex-math id="math-267"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula> would guarantee a win for <inline-formula><tex-math id="math-268"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle P _ { 2 } \end{document} ]]></tex-math></inline-formula>because neither of these choices lead to an arithmetic progression in blue. Hence, <inline-formula><tex-math id="math-269"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda = 2 \end{document} ]]></tex-math></inline-formula>.</p><p>Note that we only calculate the value of λ after <inline-formula><tex-math id="math-270"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle P _ { \mathrm { 2 } } \mathrm { ^ { 3 } s } \end{document} ]]></tex-math></inline-formula> choice at the end of <inline-formula><tex-math id="math-271"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> Meaning that in order for Player 2 to win, <inline-formula><tex-math id="math-272"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \end{document} ]]></tex-math></inline-formula> must be of value at least 2. If <inline-formula><tex-math id="math-273"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda = 1 \end{document} ]]></tex-math></inline-formula> then Player 2 can only avoid blue 3-term arithmetic progression by colouring a particular integer <italic>i</italic> at <inline-formula><tex-math id="math-274"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula>. However, this may lead to the scenario where Player 1 colours <italic>i</italic> at <inline-formula><tex-math id="math-275"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> and thus forcing Player 2 to lose (forming a blue 3-term arithmetic progression at <inline-formula><tex-math id="math-276"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } ) \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Lemma 3.5.</bold><italic></italic><inline-formula><tex-math id="math-277"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I f \lambda \geq 2 \end{document} ]]></tex-math></inline-formula><italic> , Player 2 wins.</italic></p><p><italic>Proof.</italic> The parameter <inline-formula><tex-math id="math-278"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> implies that there exist integers <inline-formula><tex-math id="math-279"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i _ { 1 } , \dots , i _ { \lambda } \end{document} ]]></tex-math></inline-formula> such that when coloured by Player 2 at <inline-formula><tex-math id="math-280"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } . \end{document} ]]></tex-math></inline-formula> , he can always avoid a monochromatic arithmetic progression and thus leads to the defeat of Player 1, i.e., Player 1 will form a red monochromatic 3-term arithmetic progression (because <inline-formula><tex-math id="math-281"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( 3 ; 2 ) = 9 ) \end{document} ]]></tex-math></inline-formula>. Given that Player 1 can only colour a single integer at <inline-formula><tex-math id="math-282"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 7 } \end{document} ]]></tex-math></inline-formula> , there is still at least one uncoloured integer amongst <inline-formula><tex-math id="math-283"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i _ { 1 } , \dots , i _ { \lambda } \end{document} ]]></tex-math></inline-formula> for <inline-formula><tex-math id="math-284"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle P _ { 2 } \end{document} ]]></tex-math></inline-formula> to choose at <inline-formula><tex-math id="math-285"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula> to remain undefeated. □</p><p>We are now well-equipped to prove our main result.<target id="anchor-0a3125b1-f31f-4717-9244-ecb45d6444ca" target-type="reference-target"/></p><p><bold>Theorem 3.6.</bold><italic>In a 3-AVOID-AP game on </italic>[1, 9]<italic>, Player 2 always has a winning strategy.</italic></p><p><italic>Proof.</italic> Suppose Player 1 colour integers with red and Player 2 colour integers with blue. In each of the cases below, if Player 2 did not form a blue 3-term arithmetic progression after his turn in <inline-formula><tex-math id="math-286"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula>, then by van der Waerden theorem where <inline-formula><tex-math id="math-287"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle w ( 3 ; 2 ) = \end{document} ]]></tex-math></inline-formula><inline-formula><tex-math id="math-288"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 9 , P _ { 1 } \end{document} ]]></tex-math></inline-formula> will definitely form a red 3-term arithmetic progression after <inline-formula><tex-math id="math-289"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 9 } \end{document} ]]></tex-math></inline-formula> which is the last turn. Hence, to show that <inline-formula><tex-math id="math-290"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle P _ { 2 } \end{document} ]]></tex-math></inline-formula> has a winning strategy, we want to show that <inline-formula><tex-math id="math-291"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> after <inline-formula><tex-math id="math-292"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>, then Player 2 will have at least two possible choices in <inline-formula><tex-math id="math-293"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula> and remain undefeated (i.e. not form a blue 3-term arithmetic progression). Here, we investigate the possible choices of the two players in each turn.</p><p><bold>Turn 1</bold><inline-formula><tex-math id="math-294"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( T _ { 1 } ) \end{document} ]]></tex-math></inline-formula> : Player 1 picks an integer and colours it with red.</p><p><bold>Turn 2</bold><inline-formula><tex-math id="math-295"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \left( T _ { 2 } \right) ; \end{document} ]]></tex-math></inline-formula> : Player 2 colours 1 with blue. If 1 was coloured by Player 1, then Player 2 colours 9 with blue. Now, relabel those integers <inline-formula><tex-math id="math-296"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle i 1 0 - i \end{document} ]]></tex-math></inline-formula> for <inline-formula><tex-math id="math-297"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 1 \leq i \leq 9 \end{document} ]]></tex-math></inline-formula> After relabelling, 1 is coloured with blue. Note that the relabelling can be reversed. If a monochromatic 3-term arithmetic progression after relabelling is formed after some turns, then by reversing the relabelling, we still have a monochromatic 3-term arithmetic progression after the reversing process. So, we may assume that 1 is coloured with blue.</p><p><bold>Turn 3</bold><inline-formula><tex-math id="math-298"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( T _ { 3 } ) \end{document} ]]></tex-math></inline-formula> : Player 1 colours his second integer.</p><p>Turn 4 <inline-formula><tex-math id="math-299"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( T _ { 4 } ) \end{document} ]]></tex-math></inline-formula> : Before Player 2 colours his second integer, two integers are already coloured by Player 1 with red. We first consider the following cases that depend on the choices of Player 1:</p><p><bold>Case 4.1</bold>: <inline-formula><tex-math id="math-300"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 4 } = I _ { 7 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 8, and then at <inline-formula><tex-math id="math-301"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 6 if it is uncoloured or 9, otherwise. By checking the uncoloured integers after <inline-formula><tex-math id="math-302"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>, we see  that <inline-formula><tex-math id="math-303"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Case 4.2</bold>: <inline-formula><tex-math id="math-304"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 7 } = I _ { 8 } = 1 \end{document} ]]></tex-math></inline-formula>. Player 2 colours 4, and then at <inline-formula><tex-math id="math-305"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 9. This gives us <inline-formula><tex-math id="math-306"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . Note that at <inline-formula><tex-math id="math-307"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } . \end{document} ]]></tex-math></inline-formula> , 9 must be uncoloured otherwise Player 1 loses.</p><p><bold>Case 4.3</bold>: <inline-formula><tex-math id="math-308"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 4 } = I _ { 8 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 7, and then at <inline-formula><tex-math id="math-309"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 6. This gives us <inline-formula><tex-math id="math-310"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . Note that at <inline-formula><tex-math id="math-311"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } . \end{document} ]]></tex-math></inline-formula> , 6 must be uncoloured otherwise Player 1 loses.</p><p><bold>Case 4.4</bold>: <inline-formula><tex-math id="math-312"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 3 } = I _ { 6 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 2, and then at <inline-formula><tex-math id="math-313"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 4 if it is uncoloured or <inline-formula><tex-math id="math-314"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ^ { 7 , } \end{document} ]]></tex-math></inline-formula> otherwise. By checking the uncoloured integers after <inline-formula><tex-math id="math-315"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , we see that <inline-formula><tex-math id="math-316"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Case 4.5</bold>: <inline-formula><tex-math id="math-317"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 2 } = I _ { 3 } = 1 \end{document} ]]></tex-math></inline-formula>. Player 2 colours 9, then in <inline-formula><tex-math id="math-318"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 6 if it is uncoloured or 8 otherwise. In either case, Player 2 colours 4 in <inline-formula><tex-math id="math-319"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Case 4.6</bold>: <inline-formula><tex-math id="math-320"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 2 } = I _ { 6 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 3, and then at <inline-formula><tex-math id="math-321"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 8 if it is uncoloured or 9, otherwise. This gives us <inline-formula><tex-math id="math-322"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Case 4.7</bold>: <inline-formula><tex-math id="math-323"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 2 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 3, and then at <inline-formula><tex-math id="math-324"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 6 if it is uncoloured or 8, otherwise. This gives us <inline-formula><tex-math id="math-325"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p><bold>Case 4.8</bold>: <inline-formula><tex-math id="math-326"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 3 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 2, and then at <inline-formula><tex-math id="math-327"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 6. This gives us <inline-formula><tex-math id="math-328"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . Note that at <inline-formula><tex-math id="math-329"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } , 6 \end{document} ]]></tex-math></inline-formula> must be uncoloured otherwise Player 1 loses.</p><p><bold>Case 4.9</bold>: <inline-formula><tex-math id="math-330"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 6 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 8 at <inline-formula><tex-math id="math-331"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 2 at <inline-formula><tex-math id="math-332"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } . \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 3 at <inline-formula><tex-math id="math-333"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 4 at <inline-formula><tex-math id="math-334"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours <inline-formula><tex-math id="math-335"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle 7 \end{document} ]]></tex-math></inline-formula> at <inline-formula><tex-math id="math-336"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 5 at <inline-formula><tex-math id="math-337"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , \end{document} ]]></tex-math></inline-formula> then Player 2 colours 3 at <inline-formula><tex-math id="math-338"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> If Player 1 colours 7 at <inline-formula><tex-math id="math-339"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 4 at <inline-formula><tex-math id="math-340"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . In either case, <inline-formula><tex-math id="math-341"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula></p><p><bold>Case 4.10</bold>: <inline-formula><tex-math id="math-342"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 4 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours <inline-formula><tex-math id="math-343"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ^ { 7 , } \end{document} ]]></tex-math></inline-formula> and then at <inline-formula><tex-math id="math-344"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 2 if it is uncoloured or 3, otherwise. This gives us <inline-formula><tex-math id="math-345"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula></p><p><bold>Case 4.11</bold>: <inline-formula><tex-math id="math-346"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 7 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 4, and then at <inline-formula><tex-math id="math-347"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> colours 8. This gives us <inline-formula><tex-math id="math-348"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . Note that at <inline-formula><tex-math id="math-349"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } , 8 \end{document} ]]></tex-math></inline-formula> must be uncoloured otherwise Player 1 loses.</p><p><bold>Case 4.12</bold>: <inline-formula><tex-math id="math-350"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 8 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 6 at <inline-formula><tex-math id="math-351"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 2 at <inline-formula><tex-math id="math-352"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 3 at <inline-formula><tex-math id="math-353"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 3 at <inline-formula><tex-math id="math-354"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 2 at <inline-formula><tex-math id="math-355"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 4 at <inline-formula><tex-math id="math-356"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 7 at <inline-formula><tex-math id="math-357"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } . \end{document} ]]></tex-math></inline-formula> If Player 1 colours 5 at <inline-formula><tex-math id="math-358"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 7 at <inline-formula><tex-math id="math-359"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . In either case, <inline-formula><tex-math id="math-360"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula></p><p><bold>Case 4.13</bold>: <inline-formula><tex-math id="math-361"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle I _ { 5 } = I _ { 9 } = 1 \end{document} ]]></tex-math></inline-formula> . Player 2 colours 6 at <inline-formula><tex-math id="math-362"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> . If Player 1 picks 2 at <inline-formula><tex-math id="math-363"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , \end{document} ]]></tex-math></inline-formula> then Player 2 colours 3 at <inline-formula><tex-math id="math-364"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 3 at <inline-formula><tex-math id="math-365"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , \end{document} ]]></tex-math></inline-formula> then Player 2 colours 2 at <inline-formula><tex-math id="math-366"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If Player 1 colours 4 at <inline-formula><tex-math id="math-367"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 7 at <inline-formula><tex-math id="math-368"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> If Player 1 colours 8 at <inline-formula><tex-math id="math-369"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then Player 2 colours 3 at <inline-formula><tex-math id="math-370"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . In either case, <inline-formula><tex-math id="math-371"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula></p><p>For the remaining cases, we may assume that</p><p>(i) any two or all integers in <inline-formula><tex-math id="math-372"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ 4 , 7 , 8 \} \end{document} ]]></tex-math></inline-formula> remain uncoloured by Player 1 before <inline-formula><tex-math id="math-373"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula></p><p>(ii) any two or all integers in <inline-formula><tex-math id="math-374"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ 2 , 3 , 6 \} \end{document} ]]></tex-math></inline-formula> remain uncoloured by Player 1 before <inline-formula><tex-math id="math-375"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , and</p><p>(iii) 9 is uncoloured by Player 1 before <inline-formula><tex-math id="math-376"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> .</p><p>So, at <inline-formula><tex-math id="math-377"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 4 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 9 with blue. At <inline-formula><tex-math id="math-378"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , Player 1 picks his third digit. In this scenario, <inline-formula><tex-math id="math-379"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle P _ { 2 } \end{document} ]]></tex-math></inline-formula> would have to avoid integer 5 in all the remaining turns (i.e. <inline-formula><tex-math id="math-380"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-381"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 8 } ) \end{document} ]]></tex-math></inline-formula>. Before <inline-formula><tex-math id="math-382"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 1 has coloured 3 integers and these three integers cannot be {2, 3, 4} or {6, 7, 8} or {4, 6, 8}.</p><p>Furthermore, at least one of the integers in {4, 7, 8} and at least one of the integers in {2, 3, 6} are uncoloured before <inline-formula><tex-math id="math-383"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>. Suppose that after <inline-formula><tex-math id="math-384"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , ~ 4 , 6 , 7 \end{document} ]]></tex-math></inline-formula> are coloured with red. Now, at <inline-formula><tex-math id="math-385"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } , \end{document} ]]></tex-math></inline-formula> Player 2 colours 8 with blue. Since 2,3 are still uncoloured after <inline-formula><tex-math id="math-386"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , we have <inline-formula><tex-math id="math-387"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>. So, we may assume that before <inline-formula><tex-math id="math-388"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , the three integers coloured by Player 1 cannot be {2, 3, 4} or {6, 7, 8} or {4, 6, 8} or {4, 6, 7}. Now, at <inline-formula><tex-math id="math-389"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } . \end{document} ]]></tex-math></inline-formula> , Player 2 colours 2 with blue if it has not been coloured by Player 1.</p><p>If two of the integers in {4, 7, 8} are uncoloured, then <inline-formula><tex-math id="math-390"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> because <inline-formula><tex-math id="math-391"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( I _ { 1 } , I _ { 2 } , I _ { 9 } ) = \end{document} ]]></tex-math></inline-formula><inline-formula><tex-math id="math-392"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( 2 , 2 , 2 ) \end{document} ]]></tex-math></inline-formula> after <inline-formula><tex-math id="math-393"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> . If 7, 8 are coloured with red, then after <inline-formula><tex-math id="math-394"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } , \end{document} ]]></tex-math></inline-formula> , 4 and 6 are uncoloured, thus <inline-formula><tex-math id="math-395"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . If 4, 8 are coloured with red, then after <inline-formula><tex-math id="math-396"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , 6 and 7 are uncoloured, thus <inline-formula><tex-math id="math-397"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . If 4, 7 are coloured with red, then after <inline-formula><tex-math id="math-398"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , 6 and 8 are uncoloured, thus <inline-formula><tex-math id="math-399"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p>Suppose 2 has been coloured by Player 1 but 3 has not. If two of the integers in <inline-formula><tex-math id="math-400"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \{ 4 , 7 , 8 \} \end{document} ]]></tex-math></inline-formula> are uncoloured, then at <inline-formula><tex-math id="math-401"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>, Player 2 colours 3 with blue. We have <inline-formula><tex-math id="math-402"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> because <inline-formula><tex-math id="math-403"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ( I _ { 1 } , I _ { 3 } , I _ { 9 } ) = ( 2 , 2 , 2 ) \end{document} ]]></tex-math></inline-formula> after <inline-formula><tex-math id="math-404"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula>. Suppose that after <inline-formula><tex-math id="math-405"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } , \ 2 , 7 , 8 \end{document} ]]></tex-math></inline-formula> are coloured with red. Now, at <inline-formula><tex-math id="math-406"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 4 with blue. Since 3,6 are still uncoloured after <inline-formula><tex-math id="math-407"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , we have <inline-formula><tex-math id="math-408"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula> . If <inline-formula><tex-math id="math-409"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle ^ { 2 , 4 , 8 } \end{document} ]]></tex-math></inline-formula> are coloured with red after <inline-formula><tex-math id="math-410"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then at <inline-formula><tex-math id="math-411"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } . \end{document} ]]></tex-math></inline-formula> , Player 2 colours 7 with blue. If 2,4,7 are coloured with red after <inline-formula><tex-math id="math-412"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 5 } \end{document} ]]></tex-math></inline-formula> , then at <inline-formula><tex-math id="math-413"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , Player 2 colours 8 with blue. In either case, 3 and 6 are still uncoloured after <inline-formula><tex-math id="math-414"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle T _ { 6 } \end{document} ]]></tex-math></inline-formula> , so we have <inline-formula><tex-math id="math-415"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \lambda \geq 2 \end{document} ]]></tex-math></inline-formula>.</p><p>Suppose 2 and 3 have been coloured by Player 1, then this case as in Case 4.5 where Player will have a winning strategy.</p><p>This completes the proof.<target id="anchor-fe254d85-d0d9-4d5b-b32c-67c1305a93e5" target-type="reference-target"/></p><p><bold>Theorem 3.7.</bold><italic>In a 3-AVOID-AP game on </italic>[1, 9]<italic>, Player 2 always wins and </italic><inline-formula><tex-math id="math-416"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { 9 } ( 3 ) = \end{document} ]]></tex-math></inline-formula><italic> 9.</italic></p><p><italic>Proof.</italic> This follows immediately from Lemma <xref ref-type="custom" custom-type="reference-target" rid="anchor-3184727f-fc1b-4620-8134-da95d74aa10f">3.4</xref> and Theorem <xref ref-type="custom" custom-type="reference-target" rid="anchor-0a3125b1-f31f-4717-9244-ecb45d6444ca">3.6</xref>.</p></sec></sec><sec id="sec-5"><title>4. Conclusions</title><p>In this paper, we have found <inline-formula><tex-math id="math-417"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 3 ) = 5 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-418"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( 4 ) = 7 \end{document} ]]></tex-math></inline-formula>. We also have shown that in a <italic>k</italic>-AVOID-AP game on <inline-formula><tex-math id="math-419"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula>, where n is suficiently large, Player 2 always has a winning strategy if <italic>n</italic> is even. New techniques might need to be developed in order to find the winning strategy for either Player 1 or 2 when n is odd. Besides that, <inline-formula><tex-math id="math-420"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \hat { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> for <inline-formula><tex-math id="math-421"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle k \geq 5 \end{document} ]]></tex-math></inline-formula> and <inline-formula><tex-math id="math-422"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle \tilde { w } _ { n } ( k ) \end{document} ]]></tex-math></inline-formula> are also remained unknown. For <italic>k</italic>-AP game, it will be interesting to determine if there is a strategy for Player 1 to win the game.</p><p>We only consider 2-players games in this paper. So, it will be interesting to consider <italic>r</italic>-players games where each player is given one colour. Hence, this will be an <italic>r</italic>-colouring of<inline-formula><tex-math id="math-423"><![CDATA[ \documentclass{article} \usepackage{amsmath} \begin{document} \displaystyle [1, n] \end{document} ]]></tex-math></inline-formula>. Questions that can be asked are whether some of the results in this paper can be extended to <italic>r</italic>-players games.</p></sec></body><back><ack><title>Acknowledgement.</title><p>This project is supported by Fundamental Research Grant Scheme (FRGS)- FRGS/1/2020/STG06/SYUC/03/1 by Malaysia Ministry of Higher Education and Sunway University Publication Support Scheme.</p></ack><ref-list><title>REFERENCES</title><ref id="BIBR-1"><element-citation publication-type="journal"><article-title>Beweis einer baudetschen vermutung</article-title><source>Nieuw Arch. 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