TsumegoFromGames138/Solution
![[Diagram]](../../diagrams/10/71009928458d8e3a967712223bdeedfb.png)
Black to play & kill the upper right group
is necessary to prevent White from forming a ko. After
,
is the vital point: White can't play 5 due to shortage of liberties, and it becomes a false eye. If white plays any other move after
, black plays at
.