|Table of contents||Table of diagrams
Diag. 1.1 Main line of solution
Diag. 1.2 Main line of solution - continued (1)
Diag. 1.3 Main line of solution - continued (2)
Diag 2.1 Different try by White
Diag 3.1 Mistake by Black
Diag 3.2 Continuation
Diag 3.3 Continuation
Diag 4.1 Mistake by Black
Diag 5.1 Mistake by Black
Diag 5.2 One possible continuation
Malcolm: is not easy to spot I think. is the strongest resistance it seems. It threatens to cut at , hence Black protects at . then threatens to kill by making a bulky five or an eye inside Black's shape. But Black has a special technique to resist. First she makes the exchange for .
Then, serves to prevent White from making a bulky five. After , Black plays in leading to the position in the next diagram.
Now it's White's turn. White must prevent Black from playing at a which gives Black a living shape. However a white move at a would go back to the position that already occurred at the end of Diag. 1.1.
Now if the ruleset has a superko rule, White is not allowed to play at a as it makes a position that already occurred. So Black lives in this case. However, this corner does provide White with almost unlimited ko threats for the rest of the game.
If the ruleset does not have a superko rule, White can play at a. The position can then cycle indefinitely. If the players do start to play out this cycle, the game is declared void. For more details, see the SL page eternal life, which discusses a similar shape.
Malcolm: White may try after in Diag 1.1. But after Black is alive. (In a previous version I mistakenly gave at a, but that lets White make a ko).
The natural move of is a mistake. , at the vital point, threatens to connect out at a.
But if Black blocks at , reduces Black's eye space. Black is dead:
For once, the 1-2 point doesn't work. White cuts and captures the two stones.