Chinese rules final ko

[hexahedron]

Today, in the EGF pro qualification game between Lukas and Stanislaw today (Chinese rules, 7.5 komi), KataGo made a surprising claim about M19 being a losing move for black. It turns out the reason is that under Chinese rules if you have a ton of ko threats, you can sometimes gain an extra point by delaying winning a final ko, as I believe was discussed in another thread on this forum too that I don’t recall the title of at the moment. This endgame turns out to be a fascinating case study of that.

Basically, if the dame parity allows you to get the last dame, AND you have so many ko threats that you can refuse to finish a ko until after all dame are filled (even if the opponent captures the ko in between every dame, you still have enough threats) then you can gain an extra 2 points.

Here is the analysis. One of the variations has a wonderful tesuji by which black manufactures a ko out of thin air, purely to be able to pull off this trick.
http://eidogo.com/#GKwOZx3n
EGF1-2.sgf (11.3 KB)

[claire_yang]

The technique called 粘劫收後 in my reply

Is an endgame ko worth more in Chinese rules than in Japanese rules?

This tactic has a name in Chinese Go terminology called - 粘劫收後, filling (by winning) the ko and get the last play/dame. It’s under the circumstance where one side can start the ko and has more (valid) ko threats and can fill the last dame. Keep the ko going but don’t actually use ko threats, instead playing “neutral points” as if they are ko threats. If the opponent play the ko, keep playing ko. If the opponent fills dame, you also fill dame (treating dame move like a ko). When you get the last…