TsumegoFromGames127/Attempts

White to move, Black played  

Herman: After , a and b are miai, as are c and d

tapir: This gives black the chance to correct his mistake and save the four stones. Black can't cut anyway (he can cut, but white will live on the edge). at is my solution. Simple but nice.

White to move, Black played  

Herman: With , black can make ko here. Now if white a, black b results in ko for the life of the group on the right, while white b, black a results in a ko for the status of all the circled stones. Not an easy ko for black, but better than just defending with . So it is up to white, really. If white needs those center stones to win the game, he should play your and get into this ko. If he just needs to live, then my is better :-)

Herman: Ah, and on a further note: white will only get into this ko if he he needs the center stones to win the game. Which also means that after takes the ko, at a is probably a valid ko threat, because white cannot afford to let black save those stones...

tapir: Oh. :)