(;
GM[1]
SZ[19]
AW[dc][ce][cp][po][qn][pm][qi]
AB[eq][pq][nq][qp][qo][qg][qd][oc]
LB[qg:1][ql:A]
C[Problem 80. White to play.  

Black has just played 1, threatening to invade at A. How should White respond ? ]
(;W[jc]
LB[oi:A]

TE[2]
C[Correct Answer.  

Locally, White A is the proper move, but, taking the whole board into account, White should extend from her corner enclosure to 1. ]
;B[ql]
C[Even if Black invades at 2, ... ]
;W[rm]
C[... White can fight and get a reasonable result. ]
(;B[pj]
C[If Black then goes for thickness with the sequence from 4 ... ]
;W[qj];B[qk];W[rk];B[rl];W[sl];B[rj];W[sk];B[pi];W[ri];B[qh];W[rh];B[rg]
C[... to 16, White's group is safe and ... ]
;W[ol]
TR[jc]
C[... the marked white stone and 17 neutralise Black's thickness. <= ]
)
(;B[rj]
LB[pj:@]
C[Variation.  

Instead of 4 at @, Black could go for territory with 4 ... ]
;W[pk];B[pj]
C[... and 6 here. ]
;W[qj];B[qk];W[ok];B[ri];W[op];B[oq];W[qh];B[rh];W[oi]
C[However, White settles her stones and gets thickness with the sequence to 15. (See Get Strong at Invading, Problems 27, 30, 33, 36, 39, and 42 for other versions of this joseki.) <= ]
))
(;W[oi]
TR[qg]
C[Failure.  

White 1 is the proper move, but this makes the marked stone a forcing move and ... ]
;B[ic]
C[... Black can take the big point of 2. ]
(;W[og]
C[If White 3, ... ]
;B[fc]
C[... Black extends to 4. <= ]
)
(;W[gc]
C[If White 3 here, ... ]
;B[og]
C[... Black jumps to 4. <= ]
))
)