(;
GM[1]
SZ[19]
AW[dd][cf][ci][cp][dq][gq][po][pn][qn][qj][oc][pf]
AB[ck][cn][en][nq][pq][qp][qo][qd][qg][qf][fc][id][lc]
C[Problem 158. White to play.  

White's two stones in the upper right are floating without a base. How should White strengthen them ? ]
(;W[qc]
TR[qf][pf]

TE[2]
C[Correct Answer.  

Since White exchanged the marked stones before attaching at 1, ... ]
;B[rc]
C[... Black is now forced to follow the joseki with 2 ... ]
;W[pd];B[qe]
C[... and 4. ]
;W[qb]
C[After descending to 5, White has made a base for her stones. All her groups are now safe. <= ]
)
(;W[db]
LB[jq:A]
C[Failure.  

Territorially, White 1 and White A are big moves, but ... ]
;B[qc]
LB[db:1]
C[... Black will descend at 2 and the two white stones are left floating in the center without a base. Before any other move, White 1 at 2 is absolutely essential. <= ]
)
)