Tsumego From Games 37 / Solution

The key point  

is the key point. After this White can either try to fight a ko which she cannot win (taking the whole board into account) or just let Black live.

Peaceful - Black lives  

If White chooses the simple variant and lets Black live, then capturing is a good point. White makes enough territory below to make the game close. (Bill pointed out that is better endgame technique than a).

Fighting the ko  

If White persists on trying to kill Black and plays through , then brings on the ko. Note that Black is the first to capture so White has to find the first ko threat.

Comparing with the peaceful variant it should immediatly become clear that White has to find very large ko-threats to make up for the difference. The problem is that Black has so many internal ko threats.

Ko threats (1) (8 at 5, 9 at )  

Each Black play is a ko threat.

Ko threats (2)  

If White persists then the ko threats , even make some additional points. By now Black has played some 10 internal ko threats. Try to find 10 ko threats for White which are at least as large as losing the ko (Black captures another 7 white stones) plus make up for the points around which were White's territory in the peaceful variant.

You won't find enough ko threats.

So White is clearly better off not fighting the ko, but letting Black live.

See /Attempts for some failures and an interesting "long sequence".

-- Dave, Arno, unkx80