HermanHiddema/gigago-Noether67 analysis

Sub-page of HermanHiddema

Position from the PGETC match between gigago (Gilles van Eeden) and Noether67 (Stjepan Medak). The players were under the impression that this was triple ko and the game was stopped.

[edit]

Game position

Although there are three ko mouths, this is not a true triple ko.

In a true triple ko, both players are always forced to move or they will lose the ko.

In this position, white is not forced to move, as black has no way to resolve the current position

White however, also can never capture the black stones due to the three ko mouths.

So how is this position evaluation under Japanese rules?

[edit]

Liberties filled

First off, suppose white fills the outside liberties with the two marked stones. (NOTE: black should not let this happen, see below)

Then, under Japanese rules, we enter a phase where the life and death status of stones is determined (article 9.2 and article 7.2 of the J89 rules).

During the determination of life and death, ko threats do not exist. A player can only retake a ko after passing and nominating a specific ko to retake.

In the given position, we must do this for both players. ie. first we determine whether black is dead, then we determine whether white is dead.

[edit]

Is black dead?

During determination of life and death under J89, play goes as given. After , black has no legal moves, as cannot be retaken. Black can only pass and nominate the to be retaken, but white will capture.

Conclusion: Black is dead.

[edit]

Is white dead?

During determination of life and death under J89, play goes as given. After , black has no legal move. Black can pass and nominate to retake , but then white will also pass and nominate to retake . After both players do so, the initial position is reached and no progress has been made.

Effectively, from white's perspective this functions as a double ko seki

Conclusion: White is alive

Final conclusion: If white fills the ouside liberties, black is dead, white is alive.

This means that the players were mistaken that this is triple ko. In fact, if the liberties get filled, black is simply dead, much in the same way that eg. bent four in the corner is dead. And much like bent four in the corner, black is only dead after the final passes of the game. White cannot force a capture during the game. The players could have continued playing in this case and could have scored the game at the end by removing the black group as dead.

So what about those outside liberties?

[edit]

Approach by white

Suppose, in the game position, white plays the approach , then what? Then black should play !

After , the position has resolved into a normal ko. White has one internal threat (capturing the two black stones in the eye), so if black takes at a, white takes at b, black fills one of the liberties in the eye, white retakes the ko stone at a, and it is a direct ko where black must find the first threat.

HermanHiddema/gigago-Noether67 analysis last edited by HermanHiddema on April 16, 2025 - 23:04

RecentChanges · StartingPoints · About

Edit page ·Search · Related · Page info · Latest diff