In problem 10357 I wondered what would happen if White attacks with the marked stone. Now it is your turn.
Thanks to MrMoto for pointing out a fatal flaw in the original solution...!
(;AB[qa]AB[pa]AB[pb]AB[qc]AB[qd]AB[qe]AB[qf]AW[oa]AW[ob]AW[pc]AW[pd]AW[pe]AW[pf]AB[rf]AB[se]AW[qg]AW[rg]AW[sg]AW[sf]AW[pg]AW[oc]AW[ra]TR[ra]C[To be fair: Black has one less liberty than in problem 10357, so watch your step.]AP[goproblems]
(;B[qb];W[sc]
(;B[sd];W[rd]
(;B[rc];W[re]
(;B[se];W[rb])
(;B[sd];W[rb])
(;B[rb];W[sb])
(;B[sb];W[rb])
(;B[sa];W[rb]))
(;B[re];W[rb]
(;B[rc];W[rd])
(;B[sb];W[rc]))
(;B[rb];W[re])
(;B[sb];W[re]))
(;B[rd];W[sd]
(;B[sb];W[re]C[Ko])
(;B[rc];W[sb])
(;B[rb];W[sb]
(;B[re];W[rc])
(;B[rc];W[re])
(;B[sa];W[re]MA[se]MA[ra]C[Dead by double ko]))
(;B[re];W[rb])
(;B[sa];W[rb]))
(;B[rc];W[sd]
(;B[rd];W[sb])
(;B[re];W[rb])
(;B[sb];W[re])
(;B[rb];W[re]))
(;B[rb]
(;W[sd]
(;B[rd])
(;B[rc];W[re])
(;B[sb];W[re])
(;B[re];W[sb]C[1000 year ko. If Black connects Black dies, White could make it seki. To really win the ko either side has to neglect several ko threats.])
(;B[sa];W[re]))
(;W[re]C[If White can win the ko White should play this to avoid the 1000 year ko, as White needs ignore less threats to win this way.]
(;B[rd];W[sd]
(;B[re];W[sb]C[Ko])
(;B[rc];W[re]C[Ko])
(;B[sb];W[re]C[Ko])
(;B[sa];W[re]C[Ko]))
(;B[sd];W[rd])
(;B[rc];W[sd])
(;B[sb];W[sd])
(;B[sa];W[sd])))
(;B[sb];W[sd]
(;B[rd])
(;B[re];W[rb]
(;B[rc];W[rd])
(;B[rd];W[rc]))
(;B[rc];W[re])
(;B[rb];W[re]))
(;B[re];W[rb]
(;B[rc];W[sd])
(;B[sb];W[rc]))
(;B[sa];W[rb]
(;B[rc];W[sd]
(;B[sb];W[re])
(;B[rd];W[re])
(;B[re];W[rd]))
(;B[rd];W[sd])
(;B[sd];W[rd]
(;B[re];W[rc])
(;B[rc];W[re]))
(;B[re];W[rc])))
(;B[rb];W[qb]
(;B[rd];W[sb]
(;B[sc];W[rc]C[Ko, White takes first.])
(;B[rc];W[sc])
(;B[qa];W[rc]))
(;B[rc];W[sb]
(;B[rd];W[sc])
(;B[sc];W[rd]))
(;B[sb];W[rd])
(;B[sd];W[sb])
(;B[sc];W[rd])
(;B[qa];W[pa];B[rd];W[sb];B[sc];W[rc]C[Ko])
(;B[pa];W[rc]
(;B[rd];W[sc])
(;B[sb];W[rd])
(;B[sd];W[sc])
(;B[sc];W[rd])
(;B[qa];W[pb])
(;B[pb];W[qa]))
(;B[sa];W[sb]))
(;B[rd]
(;W[qb]C[CHOICE]
(;B[sc];W[rb]
(;B[rc]C[A small life - safe and unconditional.RIGHT])
(;B[sb];W[rc])
(;B[sa];W[rc]))
(;B[rb];W[sb]
(;B[sc];W[rc]C[Ko, White takes first.])
(;B[rc];W[sc])
(;B[qa];W[rc]))
(;B[rc];W[sc]
(;B[rb];W[sb])
(;B[sb];W[rb]))
(;B[sb];W[rb]
(;B[sc];W[rc])
(;B[rc];W[sc])))
(;W[sc]C[White can also try this at her own expense...CHOICE]
(;B[rb];W[sb]
(;B[sd];W[qb])
(;B[qb];W[sd]
(;B[re];W[rc])
(;B[rc];W[re])
(;B[sa];W[re]MA[se]MA[ra]C[Dead by double ko]))
(;B[rc];W[qb])
(;B[sa]C[Ko]))
(;B[qb];W[sd]
(;B[sb];W[re]C[Ko])
(;B[rc];W[sb])
(;B[rb];W[sb]
(;B[re];W[rc])
(;B[rc];W[re])
(;B[sa];W[re]MA[se]MA[ra]C[Dead by double ko]))
(;B[re];W[rb])
(;B[sa];W[rb]))
(;B[sd];W[qb]
(;B[rb];W[sb])
(;B[sb];W[rb])
(;B[rc];W[rb]))
(;B[rc];W[qb]
(;B[rb];W[sb])
(;B[sb];W[rb]))
(;B[sb]
(;W[rb];B[qb];W[rc]C[Sente seki, even better. White should not play like this.RIGHT])
(;W[qb]C[CHOICE]
(;B[rb]C[Unconditional and slightly bigger.RIGHT])
(;B[rc];W[rb])
(;B[sd];W[rb])))))
(;B[sc]
(;W[rd]C[]
(;B[qb];W[sb]
(;B[sd];W[rc]
(;B[re];W[rb])
(;B[rb];W[re]))
(;B[re];W[rc]
(;B[sd];W[rb])
(;B[rb];W[sd]))
(;B[rc];W[sd]C[Sente seki. Black can capture 2 stones at S15 at the end of the game and the one White will trow in to keep it seki.RIGHT])
(;B[rb];W[sd]
(;B[sa]C[Alive!RIGHT])
(;B[re])
(;B[rc];W[re])))
(;B[rb];W[qb])
(;B[rc];W[qb])
(;B[sd];W[qb])
(;B[re];W[qb])
(;B[sb];W[qb])
(;B[sa];W[qb]))
(;W[qb]
(;B[rd];W[rb]
(;B[rc]C[RIGHT])
(;B[sb];W[rc]))
(;B[rc];W[rd])
(;B[rb];W[rd])
(;B[sb];W[rd])))
(;B[rc];W[qb]
(;B[rd];W[sc]
(;B[rb];W[sb])
(;B[sb];W[rb]))
(;B[rb];W[rd]
(;B[sb];W[sd])
(;B[sd];W[sb]))
(;B[sb];W[rb])
(;B[sc];W[rd]))
(;B[sb];W[rb]
(;B[qb]
(;W[rc])
(;W[sd]
(;B[sc];W[re])
(;B[rd];W[re]C[Ko])
(;B[rc];W[re])
(;B[re];W[rc])))
(;B[rc];W[qb])
(;B[rd];W[qb]
(;B[sc])
(;B[rc];W[sc])))
(;B[sd];W[qb];B[rb];W[sb])
(;B[re];W[qb])
(;B[sa];W[rb]
(;B[qb];W[sd]
(;B[rc];W[re])
(;B[rd];W[sc])
(;B[sc];W[re])
(;B[sb];W[re]))
(;B[rd];W[qb]
(;B[sc];W[rc])
(;B[rc];W[sc]))
(;B[sc];W[qb])
(;B[rc];W[qb])
(;B[sb];W[qb])
(;B[sd];W[qb])
(;B[re];W[qb])))