White to live. If not unconditionally at least with a favourable 2-step ko. (correction of #17910 refuted by blyx)
(;AB[ds]AB[cr]AW[dq]AW[er]AW[es]AW[fr]AB[fs]AB[gr]AB[hr]AB[gq]AB[gp]AB[fp]AB[bo]AW[ap]AW[ao]AW[an]AW[bm]AW[cn]AW[cl]AW[bl]AB[ck]AB[cj]AB[bj]AB[di]AB[dl]AB[dm]AW[dk]AW[ek]AW[el]AB[em]AB[dn]AB[do]AB[co]AW[fm]AB[fl]AB[gl]AB[fj]AB[gm]AW[fn]AW[fo]AW[eo]AW[gn]AB[hn]AB[ho]C[White need not keep all his stones alive. Also see introduction above]AP[goproblems]
(;W[cq]
(;B[bp]C[CHOICE]
(;W[bs]
(;B[dr]
(;W[cs]
(;B[ar]C[CHOICE]
(;W[bq];B[aq]
(;W[bn]
(;B[al]C[CHOICE]
(;W[ep]
(;B[ej]C[CHOICE]
(;W[dp]
(;B[fq]LB[en:X]C[CHOICE]
(;W[eq];B[bk]LB[en:X]
(;W[cp];B[fk];W[as];B[br];W[bs];B[go];W[gs]C[];B[cs]C[Blacks last ditch effort];W[as]
(;B[aq]LB[en:X]C[CHOICE]LB[cm:X]
(;W[cr]
(;B[ds]LB[en:X]LB[cm:X]C[CHOICE]
(;W[ar]C[RIGHT])
(;W[cm]C[NOTTHIS])
(;W[en]C[NOTTHIS]))
(;B[ar]LB[en:X]LB[cm:X]LB[br:X]C[CHOICE]
(;W[ds]C[RIGHT])
(;W[en]C[NOTTHIS])
(;W[cm]C[NOTTHIS])
(;W[br]C[NOTTHIS])))
(;W[ar];B[cr])
(;W[en]C[NOTTHIS])
(;W[cm]C[NOTTHIS]))
(;B[cr]LB[en:X]LB[cm:X]C[CHOICE]
(;W[aq];B[br]LB[en:X]LB[cm:X]
(;W[cs];B[dr]C[Seki is excellent for whiteRIGHT])
(;W[dr];B[cs]C[White is dead])
(;W[cm]C[NOTTHIS])
(;W[en]C[NOTTHIS]))
(;W[cs];B[dr]LB[cm:X]LB[en:X]
(;W[aq];B[br]C[Seki is excellent for whiteRIGHT])
(;W[en]C[NOTTHIS])
(;W[cm]C[NOTTHIS]))
(;W[en]C[NOTTHIS])
(;W[cm]C[NOTTHIS])))
(;W[en]C[NOTTHIS])
(;W[br];B[dr]LB[en:X]
(;W[cp];B[dj])
(;W[en]C[NOTTHIS]))
(;W[as];B[br]
(;W[bs];B[cm])
(;W[cp];B[bs];W[gs];B[go])))
(;W[cp];B[dj];W[eq];B[fk];W[as];B[br];W[bs];B[go];W[gs];B[en])
(;W[en]C[NOTTHIS])
(;W[gs];B[eq];W[br];B[dr]))
(;B[bk]C[The computer will not play this variation];W[br];B[dr];W[fq]C[RIGHT]))
(;W[eq];B[bk];W[dp];B[cm];W[br];B[dr];W[as];B[aq];W[ar];B[fk])
(;W[cp];B[dj]
(;W[dp];B[fq];W[eq];B[fk];W[as];B[br];W[bs];B[go];W[gs];B[en])
(;W[eq];B[bk];W[dp];B[fk];W[as];B[br];W[bs];B[cm])))
(;B[dp]C[The computer will not play this variation];W[eq]
(;B[bk];W[en];B[ej];W[cp]C[RIGHT])
(;B[ej];W[as];B[br];W[bs]C[Also easy for whiteRIGHT]))
(;B[eq];W[br];B[dr];W[fq];B[dp];W[cp]LB[cm:A]LB[en:B]C[And black is killed by either A or BRIGHT]))
(;W[eq];B[bk]
(;W[dp];B[ep]
(;W[cp];B[go];W[as];B[br])
(;W[as];B[br];W[bs];B[cm]))
(;W[as];B[br]
(;W[bs];B[cm])
(;W[dp];B[bs];W[cp];B[ep])))
(;W[dp];B[ep]
(;W[cp];B[go])
(;W[cm];B[bk];W[br];B[dr];W[as];B[aq];W[ar];B[go]))
(;W[cp];B[ep];W[dp];B[go]))
(;B[eq]C[The computer will not play this variation];W[br];B[dr];W[al]C[RIGHT]))
(;W[ep];B[bn];W[am];B[ej];W[dp];B[fq];W[eq];B[cm])
(;W[eq];B[bn]
(;W[am];B[cm]
(;W[dp];B[bk])
(;W[as];B[br];W[bs];B[bk]))
(;W[cm];B[am])))
(;W[br];B[dr];W[bq];B[aq])
(;W[bn];B[bq];W[br];B[dr];W[aq];B[al]))
(;B[bq]C[The computer will not play this variation];W[br];B[dr];W[ar];B[aq];W[ep]C[RIGHT])
(;B[br]C[The computer will not play this variation];W[bq];B[as];W[eq];B[aq]C[This is a good two-step ko for white];W[ar]C[This is a good 2-step ko for white, but it is probably the best overall play for blackRIGHT])
(;B[aq]C[The computer will not play this variation];W[br];B[dr];W[ar];B[bq];W[ep]C[RIGHT]))
(;W[br];B[ar]
(;W[bq];B[aq];W[as];B[aq])
(;W[cs];B[dr];W[bq];B[aq])
(;W[aq];B[bq]))
(;W[eq];B[bq];W[br];B[ar]))
(;B[bq]C[The computer will not play this variation];W[br];B[ar];W[dr]
(;B[aq];W[ep]C[White always saves one of his wing formationsRIGHT])
(;B[ep];W[aq]C[White always saves one of his wing formationsRIGHT]))
(;B[ar]C[The computer will not play this variation];W[dr]
(;B[cs];W[bq];B[aq];W[ep]C[This is better for white than the main line; he now saves bith his wing formationsRIGHT])
(;B[bq];W[br]
(;B[aq];W[ep]C[White always saves one of his wing formationsRIGHT])
(;B[ep];W[aq]C[White always saves one of his wing formationsRIGHT]))))
(;W[bq];B[bs]
(;W[aq];B[br]C[In the end black kills at A]LB[ar:A])
(;W[br];B[aq];W[as];B[cs])
(;W[dr];B[cs]
(;W[aq];B[br]LB[ar:A]C[In the end black kills at A])
(;W[br];B[aq]))
(;W[eq]LB[br:A]LB[ar:B]C[Black kills in the long run by playing A and B. No hurry.]))
(;W[br];B[bs];W[dr];B[cs];W[as];B[cs];W[bq];B[aq])
(;W[dr];B[bs]
(;W[cs]C[A direct ko is not good enough; see the introduction])
(;W[br];B[cs]
(;W[as];B[cs];W[bq];B[aq])
(;W[bq];B[aq]))))
(;B[br]C[The computer will not play this variation];W[bs]
(;B[bq];W[bp]
(;B[dr];W[eq];B[aq];W[as];B[cp];W[cs];B[ar];W[bs]C[RIGHT])
(;B[as];W[aq];B[cs];W[ar]C[RIGHT]))
(;B[bp];W[bq];B[cs];W[ar];B[as];W[aq]C[RIGHT]))
(;B[bq]C[The computer will not play this variation];W[bp]
(;B[br];W[bs]
(;B[dr];W[eq];B[aq];W[as];B[cp];W[cs];B[ar];W[bs]C[RIGHT])
(;B[as];W[aq];B[cs];W[ar]C[RIGHT]))
(;B[bs];W[ar];B[br];W[aq];B[cp]
(;W[dp];B[eq];W[dr];B[ep];W[cs])
(;W[dr];B[bn];W[am];B[bk];W[as]C[Good win for whiteRIGHT])))
(;B[bs]C[The computer will not play this variation];W[bp]
(;B[br];W[ar];B[cp];W[dr];B[bn];W[bq];B[cm];W[cs]C[RIGHT])
(;B[bq];W[ar];B[br];W[aq];B[cp];W[as];B[bn];W[am];B[cm];W[dr]C[RIGHT])
(;B[ar];W[bq]
(;B[br];W[dr]C[RIGHT])
(;B[dr];W[br]C[RIGHT])))
(;B[dr]C[The computer will not play this variation];W[br]C[RIGHT]))
(;W[bp];B[cq];W[cp];B[dp];W[ep];B[eq];W[fq];B[gs]LB[cm:X]
(;W[bn];B[dr])
(;W[br];B[dr];W[bq];B[eq];W[bs];B[ar];W[bn];B[al])
(;W[cm]C[NOTTHIS]))
(;W[bq];B[cq];W[br];B[cp])
(;W[ep];B[cq]C[Easy semeai win for black by capturing the upper 3 stones];W[cp];B[bp];W[bq];B[br]
(;W[aq];B[dp]C[Easy win in the semeai by capturing the upper 3 white stones])
(;W[ar];B[dp]C[Still an easy win in the semeai])))