Kill the marked stones !
Beware of your black group.
(Thanks to MoreKnock for his variation, but White will not sacrifice more stones to save the marked stones)
(;SZ[19]AW[ib]AW[rb]AW[sb]AW[ec]AW[fc]AW[gc]AW[hc]AW[jc]AW[kc]AW[pc]AW[qc]AW[rc]AW[cd]AW[dd]AW[hd]AW[kd]AW[ld]AW[od]AW[qd]AW[sd]AW[be]AW[de]AW[ee]AW[he]AW[ke]AW[me]AW[ne]AW[oe]AW[re]AW[cf]AW[hf]AW[if]AW[jf]AW[kf]AW[lf]AW[sf]AW[rg]AW[fh]AW[hh]AW[ih]AW[nh]AW[rh]AW[ci]AW[hi]AW[ji]AW[ki]AW[li]AW[mi]AW[oi]AW[ri]AW[kj]AW[mj]AW[kk]AW[lk]AW[rk]AW[cl]AW[am]AW[bm]AW[cm]AW[om]AW[rm]AW[dn]AW[gn]AW[fo]AW[ko]AW[cp]AW[dp]AW[gp]AW[hp]AW[sp]AW[dq]AW[eq]AW[fq]AW[hq]AW[kq]AW[rq]AW[er]AW[ir]AB[na]AB[ra]AB[bb]AB[eb]AB[fb]AB[gb]AB[kb]AB[mb]AB[ob]AB[pb]AB[qb]AB[cc]AB[dc]AB[ic]AB[lc]AB[nc]AB[oc]AB[bd]AB[id]AB[jd]AB[md]AB[pd]AB[ge]AB[ie]AB[pe]AB[qe]AB[gf]AB[qf]AB[rf]AB[hg]AB[ig]AB[jg]AB[kg]AB[lg]AB[mg]AB[qg]AB[ch]AB[jh]AB[mh]AB[ii]AB[ni]AB[hj]AB[ij]AB[nj]AB[oj]AB[fk]AB[hk]AB[ml]AB[nl]AB[pl]AB[dm]AB[em]AB[km]AB[bn]AB[cn]AB[on]AB[qn]AB[rn]AB[ao]AB[co]AB[bp]AB[fp]AB[qp]AB[aq]AB[cq]AB[gq]AB[nq]AB[oq]AB[qq]AB[cr]AB[dr]AB[fr]AB[gr]AB[hr]AB[pr]AB[es]MA[ji]MA[ki]MA[li]MA[mi]MA[kj]MA[mj]MA[kk]MA[lk]AW[bh]AB[os]AB[mr]AW[po]AW[ss]AW[qr]AW[qs]AW[rr]AW[nr]AW[or]AW[sg]AB[sh]GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]RU[Japanese]KM[0.00]PW[Blanc]PB[Noir]
(;B[kn]C[]
(;W[im]C[nice tesuji ! L6 makes P12 and G12 ladders working...Beware J7 looks like ladder breaker.CHOICE]
(;B[hm];W[jl]C[];B[in];W[hl]C[]
(;B[gl];W[jn]C[];B[jm];W[il]
(;B[gm];W[jo];B[hn];W[mn]C[Beware N6 looks like ladder breaker too.]
(;B[ln];W[lo]C[Good job M6 was the only way to make P12 ladder working and to protect the middle stones.]
(;B[lm];W[pj]C[Again a ladder breaker.]
(;B[oh];W[ng]C[]
(;B[og];W[nf]
(;B[gh];W[nk];B[ok];W[ol]
(;B[pk];W[pm]C[CHOICE]
(;B[qm];W[ql]
(;B[mk];W[mm];B[ll];W[nm]
(;B[pi];W[qj];B[mo];W[pn]
(;B[oo];W[qk]
(;B[nk];W[kl];B[oi];W[pg]
(;B[pp]C[RIGHT])
(;B[qo]C[RIGHT])
(;B[nn]C[RIGHT]))
(;B[oi];W[kl];B[nk];W[pg]
(;B[pp]C[RIGHT])
(;B[qo]C[RIGHT])
(;B[nn]C[RIGHT])))
(;B[no];W[kl];B[nk];W[qk];B[oi];W[pg])
(;B[qo];W[mp])
(;B[pp];W[mp]))
(;B[qj];W[kl]))
(;B[pi];W[mm];B[ll];W[nm];B[mk];W[qj];B[mo];W[pn]
(;B[oo];W[qk]
(;B[nk];W[kl];B[oi];W[pg]
(;B[pp]C[RIGHT])
(;B[qo]C[RIGHT])
(;B[nn]C[RIGHT]))
(;B[oi];W[kl];B[nk]))
(;B[no];W[kl];B[nk];W[qk];B[oi];W[pg])
(;B[qo];W[mp])
(;B[pp];W[mp])))
(;B[mk];W[qm]
(;B[qj];W[pi];B[qi];W[of]C[R12 pleaseFORCE];B[qh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[pf]C[Black loses the race])
(;B[pi];W[qj]C[Black dies first]))
(;B[qj];W[mm];B[ll];W[mk])
(;B[nm];W[qm];B[mk];W[nn]
(;B[pn];W[pi])
(;B[qj];W[pi];B[qi];W[of]
(;B[qh];W[pf]C[Q12 please];B[ph];W[pi])
(;B[ph];W[pi]C[Play R12 please];B[qh];W[pf]))
(;B[pi];W[qj]C[Black dies first]))
(;B[pi];W[mm];B[ll];W[mk]))
(;B[mk];W[pk];B[pi];W[mm];B[ll];W[nm]C[Black dies first])
(;B[pi];W[mm];B[ll];W[nm];B[mk];W[pk]))
(;B[gg];W[gh])
(;B[fg];W[ei]))
(;B[pi];W[mf]C[Black is dead. Please play P13 to see how.]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[mh]TR[jh];B[og];W[nf]
(;B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[lh])
(;B[fg];W[ei])
(;B[gg];W[gh]))
(;B[gh];W[nk];B[ok];W[ol]
(;B[pk];W[pm]
(;B[qm];W[ql]
(;B[pi];W[mm];B[ll];W[nm];B[mk];W[kl];B[nk];W[qk];B[qj];W[og]C[Black can't win this];B[mo];W[pn];B[oo];W[ph])
(;B[mk];W[mm];B[ll];W[nm];B[pi];W[kl];B[nk];W[qk];B[qj];W[og]C[Black can't win this];B[mo];W[pn];B[oo];W[ph]))
(;B[mk];W[qm]
(;B[og];W[nf]
(;B[qj];W[pi];B[qi];W[of]C[R12 pleaseFORCE];B[qh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[pf]C[Black loses the race])
(;B[pi];W[qj]C[Black dies first]))
(;B[pi];W[mf];B[og];W[nf]
(;B[gi];W[qj])
(;B[qj];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[lh])))
(;B[og];W[mk]))
(;B[mk];W[pk];B[pi];W[mf];B[og];W[nf]
(;B[gi];W[mm];B[ll];W[nm]
(;B[nk];W[qh]C[Black is dead with no eye])
(;B[oi];W[qh]C[Black is dead with no eye]))
(;B[nm];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[lh])))
(;B[ol];W[gg]))
(;B[pi];W[oh];B[gh];W[nk];B[ok];W[ol]
(;B[mk];W[pk];B[nk];W[nm])
(;B[pk]
(;W[mm];B[ll];W[nm];B[mk];W[kl];B[nk];W[pm]
(;B[ph];W[ql];B[qj];W[qk];B[pj];W[og])
(;B[qm];W[ql];B[qj];W[qk];B[pj];W[ph])
(;B[qj];W[ph];B[qm];W[ql]))
(;W[pm];B[mk])))
(;B[gh];W[nk];B[ok];W[ol]
(;B[pk];W[mm];B[ll];W[mk];B[nm];W[pm]C[One black group will die here]
(;B[qm];W[pn]TR[nn]TR[ql]C[miai])
(;B[pn];W[qm]TR[nn]TR[qk]C[miai]))
(;B[mk];W[pk];B[nk];W[mm];B[ll];W[nm]))
(;B[ol];W[gg]C[Black dies first]
(;B[ng];W[oh];B[og];W[qh]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[ng]TR[og]TR[jh]TR[mh]C[black is dead])
(;B[oh];W[ng]))
(;B[ng];W[oh]TR[nj]TR[kg]C[Now Black can't protect his 2 groups]))
(;B[ll]C[];W[kl];B[lm];W[pj];B[oh];W[ng]
(;B[og];W[nf];B[gh];W[nk];B[ok];W[ol];B[pk];W[pm]
(;B[mk];W[qm];B[qj];W[pi];B[qi];W[of]
(;B[qh];W[pf])
(;B[ph];W[pi]))
(;B[qm];W[nm];B[mk];W[mm];B[nk];W[ql];B[pi];W[qj]))
(;B[gh];W[nk];B[ok];W[ol];B[mk];W[pk];B[pi];W[nm]
(;B[oi];W[og])
(;B[nk];W[og])))
(;B[mm];W[lm];B[ll];W[kl];B[lm];W[pj];B[oh];W[nk];B[ok];W[ol]
(;B[pk];W[nm])
(;B[mk];W[nm])))
(;B[lm];W[mm];B[ll];W[gg]
(;B[ng];W[oh];B[og];W[qh]C[black dead])
(;B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm]TR[mf]TR[ql]C[Black can't protect both sides]))
(;B[ll];W[gg]LB[oh:L]C[ladder doesn't work])
(;B[mm];W[lm]
(;B[ll];W[kl];B[ln];W[lo];B[lm];W[pj];B[oh];W[nk];B[ok];W[ol]
(;B[pk];W[nm])
(;B[mk];W[nm]))
(;B[ln];W[lo];B[ll];W[kl];B[lm];W[pj];B[oh];W[nk];B[ok];W[ol]
(;B[pk];W[nm])
(;B[mk];W[nm])))
(;B[kl];W[ll];B[jk];W[lm];B[ik];W[ln])
(;B[lo];W[gg]
(;B[ng];W[oh];B[og];W[qh]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[ng]TR[og]TR[jh]TR[mh]C[black dead])
(;B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm])))
(;B[hn];W[gm]C[];B[jo];W[fl];B[gk];W[ej]C[Black will die first. G9 or K13 group]TR[gk]TR[jg])
(;B[jo];W[gm];B[hn];W[fl];B[gk];W[ej]C[Black will die first. G9 or K13 group]TR[gk]TR[jg]))
(;B[jm];W[il];B[gl];W[gm];B[hn];W[fl];B[gk];W[ej]C[Black will die first. G9 or K13 group]TR[gk]TR[jg]))
(;B[il];W[jl]
(;B[jm];W[hl];B[ik];W[ng]
(;B[gg];W[gh]TR[ge]TR[gf]TR[gg]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[jh]TR[mh]C[black dead])
(;B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei]
(;B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl]TR[kg]C[L13 dead])
(;B[ff];W[fj];B[eg];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl]TR[kg]C[L13 dead])))
(;B[hm];W[jm]))
(;B[jl];W[ng]
(;B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei]
(;B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl]C[];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl])
(;B[ff];W[fj];B[eg];W[fi];B[di];W[ej];B[dj];W[ek];B[dl]C[];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl]))
(;B[gg];W[gh]TR[ge]TR[gf]TR[gg]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[jh]TR[mh]C[black dies])
(;B[fg]C[];W[ei]C[Black dies first];B[eg];W[gh];B[gg];W[eh];B[dg];W[dh];B[mk];W[cg];B[kl];W[df];B[jk];W[fe];B[jj];W[gd];B[ll];W[ff];B[lh];W[mf]))
(;B[in];W[hm]
(;B[jl];W[ng];B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei];B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl]LB[hn:A]LB[ik:B]C[A and B miai])
(;B[il];W[jl];B[jm];W[hl];B[ik];W[ng];B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei];B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl])))
(;W[gg];B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm];B[nn];W[mm];B[mn];W[lm];B[ll]))
(;B[kl];W[gg]C[CHOICE]
(;B[ng];W[oh];B[og];W[qh]TR[hg]TR[ig]TR[jg]TR[kg]TR[lg]TR[mg]TR[ng]TR[og]TR[jh]TR[mh]C[black loses semeai])
(;B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol]
(;B[pm];W[nm];B[nn];W[mm])
(;B[nm];W[pm]TR[qm]TR[pn])))
(;B[jl];W[gg]C[]
(;B[ng];W[oh];B[og];W[qh]C[black loses semeai])
(;B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol]
(;B[pm];W[nm]LB[mf:B]LB[ql:A]C[Ladder doesn't work. Black can't protect A and B])
(;B[nm];W[pm])))
(;B[gh];W[jl]C[white can't be stopped])
(;B[gg];W[jl]C[White can't be stopped])
(;B[ng];W[jl]C[white can't be stopped])
(;B[ln];W[ng]LB[gh:L]C[ladder doesn't work. see solution])
(;B[im];W[gg]LB[oh:L]C[ladder doesn't work. see solution])
(;B[jm];W[gg]LB[oh:L]C[ladder doesn't work. see solution])
(;B[oh];W[jl]C[white can't be stopped])
(;B[jo];W[im]C[Nice try but it doesn't work...]
(;B[hm]
(;W[in]C[CHOICE]
(;B[il];W[gg];B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm];B[nn];W[mm]
(;B[lm];W[mn];B[mo];W[ln];B[lo];W[kn];B[kp];W[jn])
(;B[mn];W[lm];B[ll];W[ln];B[lo];W[kn];B[kp];W[jn]))
(;B[jl];W[gg]C[ladder doesn't work.]LB[oh:L];B[oh]))
(;W[gg]C[NOTTHIS];B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm];B[nn];W[mm];B[lm];W[mn];B[mo];W[ln];B[lo];W[kn];B[kp];W[jn];B[in];W[jm];B[jl];W[il];B[ik]))
(;B[jl];W[ng]LB[gh:L]C[ladder doesn't work])
(;B[jm];W[il];B[jk];W[ng];B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei]
(;B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl])
(;B[ff];W[fj];B[eg];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl]))
(;B[il];W[jm]
(;B[jl];W[gg];B[oh];W[ng];B[nf];W[og];B[of];W[ph];B[pg];W[oh];B[qh];W[pi];B[qi];W[pj];B[qj];W[pk];B[qk];W[ok];B[nk];W[ol];B[pm];W[nm];B[nn];W[mm];B[lm];W[mn];B[mo];W[ln];B[lo];W[kn];B[kp];W[jn];B[hm];W[in])
(;B[hm];W[jl]))
(;B[in];W[hm]))
(;B[lo];W[ng];B[gh];W[gi];B[fi];W[gg];B[gj];W[gh];B[eh];W[fg];B[ef];W[ei]
(;B[eg];W[fj];B[ff];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl];B[il];W[hm];B[hn];W[im];B[in];W[jm];B[jl];W[jn];B[jo];W[kn];B[kp];W[ln];B[mn];W[lm];B[ll];W[kl];B[mm];W[km])
(;B[ff];W[fj];B[eg];W[fi];B[di];W[ej];B[dj];W[ek];B[dl];W[fl];B[el];W[gk];B[dk];W[fk];B[fm];W[gl];B[gm];W[hl];B[il];W[hm];B[hn];W[im];B[in];W[jm];B[jl];W[jn];B[jo];W[kn];B[kp];W[ln];B[mn];W[lm];B[ll];W[kl];B[mm];W[km]))
(;B[kp];W[ng]C[Ladder doesn't work. see solution.]LB[gh:L]))
