DGoZ cover

Cover of DGoZ 3/2003.

A quadruple ko in an amateur game from the 2003 Frankfurt Go Tournament
(Simon Kober 16k vs Bjoern Wenzlaff 18k).
This link found on Sensei's Library.

Quadruple Ko

Sometimes a game played under Japanese rules ends in Quadruple Ko (四劫). Here some examples of the types of situations involved. See also Triple Ko and Eternal Life.

Statistics

After the 2007-06-28 game between Kono Rin and Akiyama Jiro ended in quadruple ko, Nihon Ki-in wrote
This was the 19th occurrence of a "No Result" game in history. Nihon Ki-in has recorded 168,813 games from July 24, 1924 until June 30, 2007. No Result has occurred at a rate of once in about 9,000 games.
After the 2015-04-09 game between Kono Rin and Mitani Tetsuya ended in quadruple ko, Nihon Ki-in wrote
This was the 24th occurrence of a "No Result" game in an official tournament at the Nihon Ki-in. Eleven of them were from quadruple kos, ten from triple kos, one from a quintuple ko, and two from "eternal life". No Result has occurred at a rate of once in 8261 games (0.0121%).

Contents

Games ending with "No Result" because of a quadruple ko:

Black White Date SGF
Ku Shen-yi Seng Kuan-ju 1740? sgf *
Hashimoto Yoshimi Isogawa Masao 1963-07-04 sgf *
Hotta Yozo Kubo Katsuaki 1974 sgf img
Ch'ien Yu-p'ing Kataoka Satoshi 1984-05-24 sgf *
Awaji Shuzo Liu Xiaoguang 1985-05-28 sgf *
Hoshino Masaki Cho Shoen 1992-01-29 sgf *
Enda Hideki Hane Naoki 1994-07-14 sgf *
Tsurumaru Keiichi Kawai Tetsuyuki 1995-04-26 sgf *
Tei Meiko Ishida Yoshio 1997-03-06 sgf *
Doi Makoto Hasegawa Sunao 2000-04-06 sgf *
Yu Bin Qiu Jun 2002-03-15 sgf *
Yoda Norimoto O Meien 2004-03-27 sgf *
O Meien Kim Sujun 2004-05-10 sgf *
Lee Changho Chang Hao 2005-09-11 sgf *
Kono Rin Akiyama Jiro 2007-06-28 sgf *
Lin Lixiang Chen Shiyuan 2009-03-08 sgf img
Lee Jae-woong Kim Hyen Chan 2012-09-02 sgf img
Gu Li Lee Sedol 2012-09-05 sgf *
Wang Yuanjun Lin Junyan 2013-07-23 sgf *
Lee Sedol Jiang Weijie 2014-06-05 sgf *
Zhou Junxun Chen Shiyuan 2014-11-11 sgf img
Wu Guangya Huang Yunsong 2015-06-25 sgf img

Additions and corrections are welcome. Mail to aeb@cwi.nl

Games ending in "No Result" because of a quadruple ko

An old Chinese game, Ku Shen-yi vs. Seng Kuan-ju, played around 1740, see GW 33, pp. 53-54

quadruple ko sgf

Capturing the White group around N2 suffices for Black to win, so Black has an infinite source of ko threats at N3, O4. White cannot allow Black to connect at A12, so must keep fighting the kos at A7 and A12.

Hashimoto Yoshimi vs. Isogawa Masao, 1963-07-04

quadruple ko sgf

The players cycle through the kos at E12, O18, R8, S6. There are kos at F2, E12, R13 of 1 point each, and a ko at O18 worth 2 points. If B wins the ko fights at O18 and F2, say, but W does not have to spend a stone capturing at T9, W wins by 0.5 point. So, B needs to win three of the four kos, and has the dead group at S10 as infinite source of threats.

Ch'ien Yu-p'ing vs. Kataoka Satoshi, 1984-05-24

quadruple ko sgf

There is a double ko at F17, F19, where White threatens A19 as soon as she has a liberty at F17 or F19. There is also a double ko at L1, N3, where Black threatens to capture five white stones. Black is ahead, but perhaps not enough to let White capture the group at B18 and also keep the five stones at L3.

Hoshino Masaki vs. Cho Shoen, 1992-01-29

quadruple ko sgf

There are double kos at T4/S6 and A5/C8.

Enda Hideki vs. Hane Naoki, 1994-07-14

quadruple ko sgf

There is a double ko bottom right that provides Black with an infinite source of ko threats. There are three further 1-point kos, and Black seems to think he needs to win all of them in order not to lose by 0.5 point. By my counting Black can just win.

Tsurumaru Keiichi vs. Kawai Tetsuyuki, 1995-04-26

quadruple ko sgf

The white central group doesn't have eyes, and needs either the outside connection via M8, or the snapback at J8. However, Black has infinitely many ko threats on the right hand side (if White does not answer a Black capture at S8, Black will continue and take at T7, probably killing the group at S11), and hence can defend M8 and H10 simultaneously.

Doi Makoto vs. Hasegawa Sunao, 2000-04-06

quadruple ko sgf

There is a double ko at R14, R17 and one at D5, H5. The White groups at T14 and F3 are both dead, but in order to keep them confined Black must always have either D5 or H5 and either R14 or R17. Now White can force a cycle.

Yu Bin vs. Qiu Jun, 2002-03-15

quadruple ko sgf

There is a double ko at A4, D6 and one at O10, O7. The latter serves as an infinite source of ko threats for White since Black must not allow White to get three liberties, or his group at M14 will die. That means that White can win both kos at A4 and D5 unless Black perseveres in the cycle.

Yoda Norimoto vs. O Meien, 2004-03-27

quadruple ko sgf

There is a double ko at A2, B1 and there are two further kos at F9 and R17. At F9 Black threatens to cut off the White group around H8. At R17 White threatens to kill all Blacks nearby. The double ko in the corner provides White with an unlimited number of ko threats, so that White can defend both F9 and R17. I am not sure whether Black could capture at A2, let White connect at F9, accept that the stones at L10 and S15 die but capture the White stones at H2. At first sight it looks like White would still win. If so, then Black has no choice.

Lee Changho vs. Chang Hao, 2005-09-11

quadruple ko sgf

There is a double ko at N1, N3, and there are two further kos at A7 and O14. The ko at A7 is just for 1 point. The white stones at K10 are dead with no eyes, surrounded by stones with an eye. However, as long as they are still on the board, the black group at M5 is threatened as soon as White captures at N1 or N3, and Black must capture the other of these two. Black can connect at N3 and let White have both A7 and O14 and win easily. The "No Result" outcome was a Black mistake.

Kono Rin vs. Akiyama Jiro, 2007-06-28

quadruple ko players sgf

There is a double ko at G19, E13 and a double ko at G1, M1. After each White move, White has taken three kos, after each Black move, Black has two. If Black plays tenuki, White has the time to fill a ko, and Black loses. So Black is forced to stay in the cycle. After Black has taken H19, White cannot allow Black to also take F19, so the next White move must leave Black with K2 as only liberty. This means that also White must stay in the cycle.

Gu Li vs. Lee Sedol, 2012-09-05

quadruple ko players sgf

There is a double ko at Q11, S11 and a double ko at Q13, S13. After each Black move, Black has taken three kos, after each White move, White has two. If White plays tenuki, Black has the time to fill a ko, and White loses. So White cannot leave the cycle. Things do not improve for Black if he leaves, so both stay.

Awaji Shuzo vs. Liu Xiaoguang, 1985-05-28

quadruple ko sgf

There is a double ko at E16, H16, and there are kos at T12 and M7. If Black wins the latter two kos, then the big White group has one eye only and dies. If Black wins the former two kos, then the White group in the upper left hand corner might die. So White cannot leave the cycle. If Black tenuki, then White can reply there. Maybe Black does not win if he leaves the cycle.

O Meien vs. Kim Sujun, 2004-08-22

quadruple ko sgf

There is a double ko at N19, N17 and a double ko at T13, T11. White cannot be allowed to capture twice on the right hand side, Black cannot be allowed to capture three times near N18, so a cycle is forced. Strange enough the game is listed as a Black win, I don't know why.

Tei Meiko vs. Ishida Yoshio, 1997-03-06

quadruple ko sgf

There is a double ko at A16, A13 that White cannot ignore (but that White can settle by spending one move at A19). As long as this exists, Black does not lose any ko fight, and can defend both at K9 and T1.

Wang Yuanjun vs. Lin Junyan, 2013-07-23

quadruple ko sgf

There is a double ko at A1,A7 and also one at N12, P13.

Lee Sedol vs. Jiang Weijie, 2014-06-05

quadruple ko sgf

Black can settle the double ko at R8/T7, but then White takes the two 1-point kos at E10 and A2, and wins by half a point.

A quintuple ko

quintuple ko sgf

Ohashi Hirofumi mentioned in a tweet a training match that ended in the quintuple go shown above. White has an unending supply of ko threats in the double ko at F1, F3. Black has an unending supply of ko threats in the double ko at G19, A17. Now they fight a ko fight at A2...

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