(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[19]KM[0.00]TM[]
PW[White]PB[Black]AW[an][bn][cn][dn][do][eo][fo][go][ho][io][dp][cq]AB[ao][bo][co][cp][ep][fp][gp][hp][ip][dq]LB[dp:A][cq:B]C[White pushed with A, Black played
elsewhere, and White cut with B.
What can Black do?]
(;B[bq]CR[bq]
;W[cr]CR[cr]
(;B[br]CR[br]
;W[dr]CR[dr]
(;B[eq]CR[eq]
;W[ap]CR[ap]
(;B[bp]CR[bp]
;W[bs]CR[bs]
(;B[ar]CR[ar]
;W[cs]CR[cs]
;B[er]LB[dp:A]CR[er]C[RIGHT
White's push at A only generates
potential ko threats.])
(;B[er]CR[er]
;W[ar]CR[ar]C[Black has given up too much.])
(;B[as]CR[as]
;W[ar]CR[ar]C[Black has given up too much.])
(;B[cs]CR[cs]
;W[ar]CR[ar]C[White is happy with a ko.]))
(;B[er]CR[er]
;W[bp]CR[bp]C[Black has given up too much.]))
(;B[er]CR[er]
;W[eq]CR[eq]
;B[fq]CR[fq]
;W[ap]CR[ap]C[White is happy with ko and an internal
ko threat.])
(;B[bs]CR[bs]
;W[eq]CR[eq]C[Black lives in the corner, but has
given too much by letting White in.])
(;B[ap]CR[ap]
;W[eq]CR[eq]C[Black lives in the corner, but has
given up too much letting White in.]))
(;B[dr]CR[dr]
;W[br]CR[br]
(;B[cs]CR[cs]
;W[ar]CR[ar]
;B[bs]CR[bs]
;W[ap]CR[ap]C[Black has given up too much.])
(;B[ar]CR[ar]
;W[ap]CR[ap]C[Black has given up too much.]))
(;B[ar]CR[ar]
;W[ap]CR[ap]
;B[bp]CR[bp]
;W[br]CR[br]
;B[aq]CR[aq]
;W[dr]CR[dr]
;B[er]CR[er]
;W[eq]CR[eq]
;B[fq]CR[fq]
;W[bs]CR[bs]C[White is ahead in liberties and
takes the corner.])
(;B[cs]CR[cs]
;W[br]CR[br]
;B[dr]CR[dr]
;W[ar]CR[ar]
;B[bs]CR[bs]
;W[ap]CR[ap]C[Black has given up too much.]))
(;B[cr]CR[cr]
;W[bq]CR[bq]
(;B[br]CR[br]
;W[dr]CR[dr]
(;B[eq]CR[eq]
;W[ar]CR[ar]
(;B[bp]CR[bp]
;W[ap]CR[ap]C[Black has given up too much.])
(;B[aq]CR[aq]
;W[ap]CR[ap]C[Black has given up too much.]))
(;B[er]CR[er]
;W[eq]CR[eq]
(;B[fq]CR[fq]
;W[dq]CR[dq]C[Black has given up too much.])
(;B[ds]CR[ds]
;W[dq]CR[dq]
;B[fr]CR[fr]
;W[fq]CR[fq]C[The four black stones can not
escape; Black has given up too much.])))
(;B[dr]CR[dr]
;W[br]CR[br]C[Black has given up too much.])))
system