(;
GM[1]
SZ[19]
AW[ce][cd][dc][fc][dp][fq][qj][qf][rd]
AB[de][cf][df][dj][cn][pp][ql][pd][nc]
TR[rd]
C[Problem 117. Black to play.  

White has just played the marked stone. What should Black do ? ]
(;B[qh]
TE[2]
C[Correct Answer.  

Black is strong at the top, this is his chance to invade at 1. Black's aim is to attack the lone white stone on the right. ]
;W[of]
C[If White jumps to 2, ]
;B[pi]
TR[qj]
C[... Black plays the diagonal move of 3. The marked stone is now under attack. ]
;W[qc]
C[If White 4, Black simply takes up position at the top with 5. ]
;B[kc];W[pj]
TR[kc]
C[After Black played the marked stone, White will run away with 6 ... ]
;B[ni];W[pl];B[qm];W[oj]
C[... to 10. ]
;B[ng]
C[Black makes shape with 11. ]
;W[mk]
C[White 12 is necessary, so ... ]
;B[nf]
LB[qm:4]
C[... Black can make a wall with 13. Although this result is not decisive for Black, he has managed to strengthen his position with 4 and White's stones still lack eyes. <= ]
)
(;B[qc]
C[Failure.  

Defending the corner with Black 1 is a passive move; Black has failed to disrupt White's position and to take the initiative. ]
;W[ph]
LB[qn:A]
C[White secures her stones with 2. Next, she aims at an invasion at A. <= ]
)
)