docs/Superko in KGS Computer Go Tournaments.htm

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  15 <h1>Superko in KGS Computer Go Tournaments</h1>
  16
  17 <p>
  18 In over a thousand games played in computer Go tournaments on KGS, ten
  19 have been ended by the Superko rule. In four of these ten cases, the
  20 effect of the rule effectively decided the result of the game.
  21 </p>
  22
  23 <h3>Forms of Superko rule.</h3>
  24
  25 <p>
  26 There are four forms of superko rule:
  27 </p><p>
  28 <table border=1 cellpadding=4 cellspacing=0>
  29 <tr><th>PSK
  30 <td><b>P</b>ositional <b>S</b>uper<b>K</b>o<td>
  31 A player may not play a stone so as to create a previous board which
  32 existed previously in the game.
  33 <td>
  34 Creation refers to the position just after the play and consequent removals.
  35 <tr><th>SSK
  36 <td><b>S</b>ituational <b>S</b>uper<b>K</b>o<td>
  37 A player may not play a stone so as to create a board position which
  38 existed previously in the game, and in which it was the opponent's turn to move next.
  39 <td>
  40 Creation refers to the position just after the play and consequent
  41 removals, and the rule also takes account of who moves next.
  42 <tr><th>NSK
  43 <td><b>N</b>atural <b>S</b>ituational Super<b>K</b>o<td>
  44 A player may not play a stone so as to create a board position which
  45 existed previously in the game, if s/he played to create it previously.
  46 <td>
  47 Creation refers to the position just after the play and consequent removals.
  48 <tr><th>ChSK
  49 <td><b>Ch</b>inese <b>S</b>ituational Super<b>K</b>o<td>
  50 A play may not recreate a previous board position from the game by means of
  51 basic ko or sending-2-returning-1. If a cycle arises in another way and neither
  52 player varies from it, the referee may declare a draw or require a replay.
  53 <td>
  54 This, according to the sixth meeting of the International Go Rules Forum, is
  55 what the Chinese rules were intended to specify.
  56 </table>
  57
  58 </p><p>
  59 All forms of superko rule refer only to playing of stones. <b>It is always legal
  60 to pass</b>, whatever form of the rule may apply.
  61 </p>
  62
  63 <h3>Chinese Rules of Go, as on KGS</h3>
  64
  65 <p>
  66 Computer Go tournaments on KGS have so far always used "Chinese Rules", as
  67 implemented on KGS.
  68 </p><p>
  69
  70 <div style="background: #FFFFBB"></div>
  71 At the time the superko code on KGS was implemented, the intention of the
  72 Chinese Rules of Go about repeated positions was unclear. Section 6, as
  73 translated into English in "<i>The Go Player's Almanac</i>", Richard Bozulich,
  74 1992, reads in full:
  75 <div class=quote>
  76 Reappearance of the same board position is forbidden throughout the game.</div>
  77 However, section 20.3 reads:
  78 <div class=quote>
  79 3. In rare situations such as triple ko, quadruple ko, eternal life, and
  80 round-robin ko, if neither side will yield, the referee may declare a draw
  81 or replay.</div>
  82 These two sections are in contradiction. The implementers of <b class=emp>KGS</b>
  83 resolved this by giving priority to the section which appears first, and
  84 <b class=emp>implemented Positional Superko</b>.
  85 </p>
  86
  87 <h3>Superko incidents in KGS Computer Go tournaments</h3>
  88
  89 <p>
  90 The application of the Positional Superko rule has several times affected a computer Go
  91 tournament game on KGS. These incidents have all be mentioned on the reports of the event,
  92 and are listed below.
  93 <table>
  94 <tr><th>date (link to report)</th><th>What happened</th><th>type of cycle</th></tr>
  95 <tr><td><a href="http://www.weddslist.com/kgs/past/6/index.html#sk">September 2005</a></td>
  96 <td>Viking5 was unable to play the move it wanted against gonzoBot, and so resigned, in
  97 what would otherwise have been a won position.</td></td>
  98   <td rowspan=9><a href="http://senseis.xmp.net/?SendingTwoReturningOne">Sending two, returning one</a></tr>
  99 <tr><td><a href="http://www.weddslist.com/kgs/past/7/index.html#sk">October 2005</a></td>
 100 <td>Dariush timed out in a won position against SlugGo, when prevented from playing
 101 the move it wanted.</td></tr>
 102 <tr><td><a href="http://www.weddslist.com/kgs/past/32/index.html#sk">November 2007</a></td>
 103 <td>Break timed out in a lost position against FirstGoBot, when prevented from playing the
 104 move it wanted.</td></tr>
 105 <tr><td><a href="http://www.weddslist.com/kgs/past/33/index.html#sk">December 2007</a></td>
 106 <td>MonteGNU timed out in a won position against WeakBot50k, when prevented from playing
 107 the move it wanted.</td></tr>
 108 <tr><td><a href="http://www.weddslist.com/kgs/past/42/index.html#sk">September 2008</a></td>
 109 <td>SimpleBot timed out in a won position against WeakBot50k, when prevented from playing
 110 the move it wanted.</td></tr>
 111 <tr><td><a href="http://www.weddslist.com/kgs/past/43/index.html#sk">October 2008</a></td>
 112 <td>HouseBot timed out in a lost position against ManyFaces, when prevented from playing
 113 the move it wanted.</td></tr>
 114 <tr><td><a href="http://www.weddslist.com/kgs/past/52/index.html#sk1">October 2009</a></td>
 115 <td>Orego timed out in a lost position against WeakBot50k, when prevented from playing
 116 the move it wanted.</td></tr>
 117 <tr><td><a href="http://www.weddslist.com/kgs/past/52/index.html#sk2">October 2009</a></td>
 118 <td>Wei2go timed out in a lost position against SimpleBot, when prevented from playing
 119 the move it wanted.</td></tr>
 120 <tr><td><a href="http://www.weddslist.com/kgs/past/59/index.html#sk">May 2010</a></td>
 121 <td>MCark timed out in a lost position against kiseki, when prevented from playing
 122 the move it wanted.</td></tr>
 123 <tr><td><a href="http://www.weddslist.com/kgs/past/61/index.html#sk">July 2010</a></td>
 124 <td>Orego timed out in a lost position against CzechBot, when prevented from playing
 125 the move it wanted.</td><td>triple ko</td></tr>
 126 <tr><td><a href="http://www.weddslist.com/kgs/past/103/index.html#sk">May 2017</a></td>
 127 <td>Julie timed out in a lost position against Aya, when prevented from playing
 128 the move it wanted.</td>
 129 <td>Sending two, returning one
 130 </table><br>
 131 Most of these positions involved the
 132 <a href="http://senseis.xmp.net/?SendingTwoReturningOne">sending two, returning one</a>
 133 shape. None of those would have been forbidden by Situational Superko or by
 134 Natural Situational Superko.
 135
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