Tsumego From Games 20

What happened during the game  

During the game, Black played . After , a and b are miai, and White is killed by shortage of liberties. White resigned soon after that.

Also dead  

provides another path of resistance. However, up to the , White is dead in bulky five. It does not matter if is played at first.

But--

Correct play by White  

The descent by is the correct move which both players failed to see. To stop White from connecting underneath Black may play at , but then ensures life. After that, a and b are miai.

The actual solution  

The real solution is actually the placement at . The best sequence is from to , which results in a rogue ko.

Dieter: the - exchange makes it a rectangular six in the corner with one outside liberty. In that case, the 1-2 point makes it ko.

Not as good  

followed by is yet another variation. Up to , it is still a ko, but the ko is worse off for White compared to the previous diagram.