Tsumego From Games 42 / Solution

Double ko death  

is the vital point.

After , if B a, then W b. If B b, then White captures four stones (connect and die).

If is at , prevents a second eye, as in variation 1.

( could also be at . If then , .)

No ko ?  

Iago not saying the previous variation doesnt work, but isnt this simpler for the same result ? if black goes for a ko, white can atari with W a unless I am missing something (number of ko threats?)

hhw: Black will first play at b. It looks to end in only ko.

Variation 1  

After secures , prevents a second eye.

and are miai.

Variation 2  

After , prevents a second eye. Even with Black cannot create an eye in the corner.

If is at , reverts to variation 1.

Bad ko  

Black takes this ko first.