Gokyo Shumyo, Section 5, Problem 18 / Attempts

White lives  

at

atulab: note that at leaves a ko and that omitting prevents black from protecting the squared stone

xela: This is not the solution. Black plays a and white is totally dead.

White to play and live by oiotoshi  

The circle point is a threatening move for White to escape out through the Black stones.

Black played at 2 to prevent a White play at Square having a follow-up move for White at 2 (and squeeze Black's liberties).

Continuation  

This White 1 could get more liberties on the outside then Black can get on the inside, so Black needs to prevent this.

Continuation  

This assumes that Black desires the KO fight rather than claiming the corner and letting White escape so Black can have sente.

Continuation  

Black must now fight to win the ko fight as the marked spaces are now miai for White to live.