Beginner Exercise 235 / Solution

Outside attack  

If , makes and miai, so Black lives. ( at is killed by at .) For White, this is a 5 point endgame play in sente (White has got an extra point at a).

(For advanced readers: this line may be preferable in the middlegame - White's outside wall has an additional eye at a, fewer cutting points, b connect in sente, and no worries about seki collapse. In a word, thick.)

Inside attack: seki 1  

After and , Black has a choice between two sekis. One way to make seki is and in the diagram. For White, this is a 6 point endgame play in sente but a cutting point appears at a.

Inside attack: seki 2  

The other way is and in this diagram. In this case, Black is emphasizing the cutting point at b.

Comparison: Black first  

(For advanced readers: If Black to play, secures 6 points of territory - a and b are miai for life and c and d are miai to save 1 point. This is a 6 point endgame play in reverse sente.)