(;AW[ra]AB[sc]AB[rb]AB[rc]AB[rd]AB[qc]AB[pc]AW[qb]AW[pb]AW[oc]AB[ob]AB[oa]AB[nb]AW[od]AW[pd]AW[pf]AB[nc]AB[og]AB[pg]AB[qg]AB[sh]AB[si]AB[sj]AW[rh]AW[ri]AW[rj]AB[ng]AW[ne]AB[nf]AW[of]AB[md]AB[me]AW[nd]AB[mc]AW[pe]AB[qd]AW[qe]AB[qf]AW[re]AB[rf]AB[sf]C[Neither side has external ko threats. Capture at least 3 stones.]AP[goproblems]
(;W[sb];B[sa]
(;W[sk]
(;B[sg]C[Black stubbornly defends the 3 stones...]
(;W[sb]C[Ko, and since White has no threats you can win it!RIGHT])
(;W[sd];B[qa]))
(;B[qa]C[Black would be better off ending the ko...];W[sg]C[But then you get the 3 stones.RIGHT]))
(;W[sg]
(;B[rg]C[Black defends the 3 stones with a vengeance.]
(;W[sb]C[Ko, and as Black has no real threats nothing can stop you from making the corner live.RIGHT])
(;W[sd];B[qa]))
(;B[qa]C[In the real world Black ends the ko...]
(;W[sk]C[but then of course you get the 3 stones.RIGHT])
(;W[rg]C[Or this.RIGHT])))
(;W[se];B[qa]C[White can't capture anything])
(;W[sd];B[qa]C[White can't capture anything])
(;W[rg];B[qa]
(;W[sg]C[Yay! You figured out Black has nothing to run to along the edge so you are probably right. And you ARE right because I say so!RIGHT])
(;W[sk];B[sg]C[Nnnnnnnnnnah.])))
(;W[sk];B[sg]
(;W[sb];B[sa];W[se];B[qa]C[White can't capture anything])
(;W[se];B[pa]C[White can't capture anything]))
(;W[se];B[pa];W[sk];B[sg]C[White can't capture anything])
(;W[sg];B[rg];W[sb];B[sa]C[Black takes the ko, and you have no threat.])
(;W[rg];B[sg];W[sb];B[sa]C[Black takes the ko, and you have no threat.]))