XuanxuanQijingProblem17/Solution

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
Diag 3.3

Main line of solution

[Diagram]

Diag. 1.1 Main line of solution

Malcolm: B1 is not easy to spot I think. W2 is the strongest resistance it seems. B3, W4 are natural. Black then makes the exchange B5 for W6.

[Diagram]

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

B1 serves to prevent White from making a bulky five. After W2, Black plays in black+triangle leading to the position in the next diagram.

[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 give precisely the position that already occurred at the end of Diag. 1.1.

Now if the ruleset has a superko rule, this means that White cannot play at a and so Black lives.

If the ruleset does not have a superko rule, White can play at a. The position can then cycle indefinitely, and is known as an eternal life position.


Relationship with the rest of the board

Malcolm: This position gives White almost unlimited ko threats for ko fights elsewhere.

Variations

[Diagram]

Diag 2.1 Different try by White

Malcolm: White may try W1 after B1 in Diag 1.1. But after B4 Black is alive.

[Diagram]

Diag 3.1 Mistake by Black

The natural move of B1 is a mistake. W2 threatens to connect out at a.

[Diagram]

Diag 3.2

But if Black blocks at B1, W2 reduces Black's eye space. Black is dead:

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

Diag 3.3

Black B1 also fails.


Conclusion

Malcolm: This is a tough dan-level problem, with interesting links to questions on superko. If one were to give it a description, it might be: "Black to play and live (by superko)".


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