This is the final game 5 of the 2nd MLily Cup between Ke Jie (Black, China) and Lee Sedol (White, Korea).

Here are a few comments on the final ko. Move 274 was played with improper timing; playing it as a ko threat would have made more sense; however, Black had more ko threats and would have won the ko nevertheless.

Chinese rules were used with 7.5 komi (full counting value) and the smallest regular winning margin B+1.5 (full counting value). Therefore the last basic endgame ko decided the winner. Move 272 played a dame as a ko threat and Black correctly replied by filling another dame, playing the dame ko fight. Afterwards, all dame were filled and so Black managed to raise the deire value of the ko to 4 points (full counting value).

If Black had made the mistake to fill the ko prematurely with move 273, and let White have the last dame intersection at 273, the deire value of the ko would only have been 2 points and White would have gained 2 points (deire counting) on the intersection at 273 to win the game by W+0.5 (full counting value, smallest regular winning margin for White).

While the area score was B+1,5, the territory score would have been W+0,5. Such is infrequent with the standard area komi 7.5.

According to https://gogameguru.com/2nd-mlily-cup-final/ Korean 9p professionals are reported to have called the ko a "half point ko". This nomenclature is bad and misleading. It ought to be called a 4/3 points ko (miai counting) or a 4 points ko (deire counting). This correct assessment warns players that they should appreciate the value of such kos more. Was Lee aware of the theory? For the theory, see also http://home.snafu.de/jasiek/kodame.pdf

EDITED

I propose this topic to be merged with this one where the games were being discussed.