Dochi Yose Tesuji

Moves 225-232  

began the brilliant sequence of moves that saved the game for Dochi.

Continuation (Moves 233-236)  

The invasion made and sente, because if White does not capture the marked stone with , Black would play at a and make a seki.

The invasion does not work if it is played after the hane-connect sequence.

White's alternative  

The other reasonable move for White is to play 4 here instead of a. Black next plays 5 and 7. If this is not sente, White has refuted Black's play.

Var 1: Black fails  

is an eye-stealing tesuji, as it makes the eye at a false, but is a good response and Black's attack runs into nothing. No matter how hard he tries, e.g. with and so on, Black cannot get a seki, ko, or anything else.

Var 2: Black succeeds  

The solution for Black is to play on White's vital point himself, with .

is forced, as a move here would be rather awkward for White. Next, is tesuji and establishes an eye in the corner. Thus the position becomes a seki.

As can be seen, if White did not reply, he would lose his corner territory (in a seki with Black). Therefore, White had to add another move to defend his territory after Black played hane-connect at the top border. The hane became Black's sente and enables him to win the game.

Variation at 233  

If Black continues playing inside, e.g. with 233 at here, there is no real difference to the game. At worst, Black has lost a ko threat.

Anonymous : is self-atari. Thus is called into question.

Anonymous2: The author should indeed reconsider