(;
GM[1]
SZ[19]
AW[db][ec][fd][fe][dd][de][df][ef][dg][co][pp]
AB[cb][bc][dc][cc][cd][ce][dq][ep][qj][pd]
C[Problem 111. Black to play.  

White has a very thick position at the top left. Black wants to counter this thickness. What is the best move for him to do this ? ]
(;B[mc]
TE[2]
C[Correct Answer.  

The large knight's move of black 1 is the ideal extension. In does not approach White's thickness too closely, yet it does not allow White to make a full extension from it. ]
;W[kc]
C[White 2 is as far as White can extend, but ... ]
;B[kd]
C[... Black will attach with 3. ]
;W[jd];B[ke];W[lc];B[md]
LB[jd:4][kc:2][lc:6]
C[White's stones at 2, 4, and 6 do not fully utilise her thickness, so they are not working efficiently. <= ]
)
(;B[jc]
C[Failure.  

Black 1 is too near to White's thickness. ]
;W[lc]
C[White will take the initiative by invading at 2. ]
;B[je];W[le];B[jg];W[lg]
LB[lc:2][le:4]
C[White now gets influence facing the right with the stones at 2, 4, and 6. <= ]
)
(;B[kc]
C[Failure.  

If Black 1 here, ... ]
;W[mc]
C[... White will invade at 2. <= ]
)
(;B[lc]
C[A bit dangerous.  

Black 1 is also a bit thin because ... ]
;W[nc]
C[... White can invade at 2. ]
;B[nd]
C[If Black next attaches at 3, ... ]
;W[od]
C[... White 4 is a good counterattack. <= ]
)
)