(;
GM[1]
SZ[19]
AW[cp][eq][nc][nd][ne][bc][ce][df]
AB[pp][od][oc][qd][pf][dh][dc][fd]
C[Problem 173. Black to play.  

Black has to make an important defensive move. Where is it ? ]
(;B[ic]
TE[2]
C[Correct Answer.  

White's three stones to the right are thick, so Black should extend tightly to 1. ]
(;W[kc]
C[If White answers with 2, ... ]
;B[jq]
C[... Black will take the big point at 3. <= ]
)
(;W[nq]
LB[ic:1]
C[Continuation.  

After Black 1, White will probably switch to the lower right and ... ]
;B[pn];W[pr];B[qq];W[kq]
C[... play the joseki to 6. ]
;B[dk]
C[After exchanging 7 ... ]
;W[cm]
C[... for 8, ... ]
;B[ng]
C[... Black will attack the three white stones by capping with 9. <= ]
))
(;B[jq]
C[Failure.  

If Black doesn't defend the top, but plays 1 instead, ... ]
;W[hc]
C[... White will seize the initiative by attacking with 2. ]
;B[ge]
C[When Black runs away with 3, ... ]
;W[ie]
C[... White makes territory at the top with 4. <= ]
)
)