XuanxuanQijingProblem17/Solution

Diag. 1.1 Main line of solution  

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 .

Diag. 1.2 Main line of solution - continued (1)  

Then, serves to prevent White from making a bulky five. After , Black plays in leading to the position in the next diagram.

Diag. 1.3 Main line of solution - continued (2)  

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.

Variations

Diag 2.1 Different try by White  

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).

Diag 3.1 Mistake by Black  

The natural move of is a mistake. , at the vital point, threatens to connect out at a.

Diag 3.2 Continuation  

But if Black blocks at , reduces Black's eye space. Black is dead:

• Next if Black a, White b
• and if Black c, White d makes a bulky four.

Diag 3.3 Continuation  

Black also fails.

Diag 4.1 Mistake by Black  

For once, the 1-2 point doesn't work. White cuts and captures the two stones.

Diag 5.1 Mistake by Black  

If Black tries , plays at the vital point. One can check that Black is dead.

Diag 5.2 One possible continuation  

For example, here lets White kill with a bulky five.