Endgame Tesuji 2

A mistake  

This seemingly innocent sequence contains a mistake. can be improved due to the presence of the marked Black stone:

Correct reply.  

This one is correct.

An example of this line of play can be seen at move 135 of game 4 of the 9th Kisei match played on 21, 22 February 1985 between Takemiya Masaki and Cho Chikun.

The result to be expected is as follows:

Follow-up.  

After the exchange /, playing on with at would be gote for White.

Hence Black can expect to get the sequence to in sente. This is two points better for Black than in the original diagram.

• • FireclawDrake: I don't really understand why playing at is gote. If it is played doesn't B have to defend at immediately?

• • Antone: I guess the idea is that white's next followup would be gote, consider this diagram where white goes with at E19, comparing it with the first diagram on this page the difference is one point of territory lost for black (and one more prisoner for white) but black gets possibly larger compensation plaing elsewhere two times with and .

tenuki, at  

One final question is whether in the first diagram becomes a mistake, given the good reply at , or whether hane is better. It is close, but is still a little better.

-- dnerra