EVENT
BOARDSIZE 19
SETUP W D16 D17 D14 C12 B13 C5 D4 G3 K3 S4 S6 T6 T7 R7 R8 S8 R9 R10 Q10 R11 S11 R12 R16 S16 R19 Q19 Q18 Q17 P17 P16 P15 N18 N17 M17 L17 L16 L18 K18 H18 H10 O9 G9 H9 C2 D3 H4 H5 C6 D7 C8 D8 
SETUP B B12 C10 C7 P3 R4 R6 R5 S5 T5 S12 T13 S14 S15 R15 Q15 Q16 R17 S17 R18 S19 O15 O14 N16 M16 O18 J18 J17 K17 K16 K15 L15 F17 F15 G11 Q9 P9 P10 P8 Q11 Q12 G10 D2 E3 F4 G4 F6 D6 H7 E7 K7 F9 
MARK A@K7
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Problem 123. Black to play.  

This is the position that arose in the game of Problem 121. Black
just jumped to A. What should White do ? 
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W 1 G7
MARK A@K7
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black A in the problem diagram is thin. When White attaches with
1 ...
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B 2 G6
W 3 H6
COM
... and cuts with 3, the black stones in the center are cut off
from their allies on the left.
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B 4 H8
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Black resists with 4, but ...
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W 5 G8
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Black must answer White 5 ...
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B 6 E8
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... with 6, ...
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W 7 K8
B 8 J6
W 9 H11
B 10 G12
W 11 L7
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... and Black's position collapses when White blocks with 11.
<=
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