Bent four in the corner exercises / Solution 3
![[Diagram]](../../diagrams/22/eeb8a0587986601e6841de66b9aff879.png)
White to play
ChrisSchack:
is the vital point, and kills unconditionally.
![[Diagram]](../../diagrams/3/b7f5cf939bb27bc0711cb3ed421995de.png)
Black tries to extend
If B tries to get more eyespace, W simply seals him in, and W cannot be prevented from playing a, then killing with an almost-fill by a bent four at the end of the game. This would only be ko if White needed to capture before game-end, to ensure a surrounding group's safety.