Four die but six live

Four stones on the third line die  

Black tries to expand his eyespace with and , but White plays and and Black dies. at a or is met with .

Special case  

If double hane on one side is sente, a ko fight for life is possible. In the diagram, and take advantage of the board edge (more specifically, the 1-2 point) to start a ko. If White protects with , makes two eyes.

Six stones on the third line: Segoe's sequences  

Bill: This appears to be White's best play, leaving a possible seki. See Segoe's sequences.

Six stones on the third line another try  

Another attempt. Black is still alive. A is correct, B seems inferior. For continuations see Analysis page.

White's option  

Robert Pauli:

The second attempt is better (sides exchanged to be compareable). The descent in the first diagram is aji keshi, it destroys the option shown here ( instead of a). If Black now can't escape or make a second eye by jumping to b with , he dies (pushing at a instead dies after b).

Sente seki  

So if Black can't hope for something at the left side, he has to play the hane , which leads to seki (missing in the analysis, by the way). The kaketsugi is better than the descent left to it since it leaves the option a (and keeps the dubious ko below indirect).

That's one point better for White than Segoe's sequence:

• after Black's hanetsugi there (left side), White lost 2 and Black counts 5: 2 + 5 = 7
• compared to White already having lost 2 here ( and a) and losing another 4 after Black's hane at a: 2 + 4 = 6

White risks nothing. If at is a threat, she still can switch to the initial sequence by answering at . White can also choose the side.

Dubious ko  

Black won't risk this ko: Black starts and White owes an approach at a, but nevertheless ko.

Five stones on the third line : B to play and live  

See The comb formation is alive and /Analysis