Xuanxuan Qijing Problem 9 / Solution

[Diagram]
 

W1 reduces the black group into 1 eye. However, can White make two eyes for the white group?

[Diagram]
 

B2 is the vital point.

B4 is to prevent seki.

After W7 White captures the four black stones. It's a bent four, but...

[Diagram]
Suprise #1  

White can't make two eyes with a due to shortage of liberties, and black is looking at the snap back at ''c'.

Making an eye around a in gote is not good enough; Black can play b and then d to make a ko.

emeraldemon: what about a play at e? This renders the snapback useless, doesn't it? Actually, as I look at it, it seems after black responds a, white must play b anyway. So maybe playing e gives one more ko threat to black for later?

[Diagram]
Suprise #2  

White makes two eye by recapturing.

See also: under the stones

[Diagram]
Optimal Sequence, B4 @ white+triangle  

Since Black cannot live should he try to capture White, then Black's best play is to capture at B2, force W3, and live with white+triangle. Should White prevent Black's two eyes @ white+triangle, then B4 @ W3 makes an unwinnable capturing race for White (Black has too many local ko threats and is ahead in liberties.)

[Diagram]
Optimal Sequence, B4 @ white+triangle  

SuperDave: White doesn't need W3 in the above diagram. White can make two eyes above if Black takes a move to threaten the eye in the corner.


Xuanxuan Qijing Problem 9 / Solution last edited by Superdave on February 26, 2018 - 01:16
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