GokyoShumyoSection3Problem90/Solution

Solution  

A tricky problem. is the clever defense to secure a ko for life. at 'a' is a mistake because...

Variation  

...White can't play at 'b' nor 'c'. Black will play at 'b' next and kill with a 5-point nakade. Then, what happens if at ?

Further Variation  

White can't defend at 'd' for shortage of liberties.