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.