Four die but six live
On the third line or in the corner on the second line a string of four stones is dead, and a string of six stones is alive. A string of five stones lives or dies according to sente. Similar proverb is Six Die But Eight Live (on second line)
Black tries to expand his eyespace with and , but White plays and and Black dies. at a or is met with .
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.
Another attempt. Black is still alive. A is correct, B seems inferior. For continuations see Analysis page.
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).
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.
Obviously black needs sente to save her stones. Black can unconditionaly live. Diagram shows the simplest solution.