(;AW[ra]AW[qb]AW[pb]AW[pc]AW[od]AW[oe]AW[pe]AW[qe]AB[pd]AB[qd]AB[qc]AB[rb]AB[oc]AB[nc]AB[nd]TR[ra]C[If White plays S19 in problem 13354 things get complicated. Find the best possible continuation.]AP[goproblems]
(;B[sb]
(;W[rd]
(;B[rc];W[se]
(;B[qa];W[pa]
(;B[ob];W[sc]
(;B[sd]C[Ko, Black takes first.RIGHT])
(;B[oa];W[sa])
(;B[re];W[sa]))
(;B[oa];W[ob]
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[na]
(;B[sd];W[sc]C[Ko, White takes first])
(;B[ma];W[sc]
(;B[oa];W[sa])
(;B[sd]C[Ko, Black takes first.RIGHT]))
(;B[sa];W[sc])
(;B[sc];W[sd])
(;B[re];W[rf];B[ma];W[sc];B[sd]C[Yeah, right.RIGHT]))
(;B[re];W[rf];B[nb];W[na];B[ma];W[sc];B[sd]C[Yeah, right.RIGHT])
(;B[na];W[nb]))
(;B[sc];W[sd])
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[re];W[rf]
(;B[ob];W[sc];B[sd]C[RIGHT])
(;B[oa];W[sc];B[sd]C[RIGHT])
(;B[sd];W[sc]C[Ko, White takes first.]))
(;B[sa];W[sc]))
(;B[pa];W[ob]
(;B[nb];W[oa])
(;B[qa];W[oa]
(;B[qa];W[sd])
(;B[sd];W[re]
(;B[qa];W[sc]C[Ko, White takes first.])
(;B[nb];W[qa])
(;B[na];W[qa]))
(;B[nb];W[qa])
(;B[na];W[qa]))
(;B[oa];W[nb])
(;B[sd];W[re]
(;B[nb];W[oa])
(;B[qa];W[oa]
(;B[qa];W[sc]C[Ko, White takes first.])
(;B[nb];W[qa])
(;B[na];W[qa]))
(;B[oa];W[nb])))
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[re];W[rf]
(;B[ob];W[sc]
(;B[sd]C[Ko, Black takes first.RIGHT])
(;B[pa];W[sa])
(;B[qa];W[sa]))
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[qa];W[pa]
(;B[ob];W[sc];B[sd]C[RIGHT])
(;B[oa];W[sc];B[sd]C[RIGHT])
(;B[sd];W[sc]C[Ko, White takes first.]))
(;B[pa];W[ob]
(;B[qa];W[oa]
(;B[qa];W[sd])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[qa])
(;B[na];W[qa])
(;B[sa];W[sc]))
(;B[sa];W[sc])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[oa])
(;B[oa];W[nb])))
(;B[ob];W[sc];B[sd]C[Ko, Black takes first.RIGHT]))
(;B[ob];W[rc])
(;B[re];W[rc]))
(;W[qa];B[rc]
(;W[rd];B[re]C[RIGHT])
(;W[re];B[ob];W[rd];B[oa]C[RIGHT])
(;W[ob];B[nb]
(;W[oa];B[na]C[RIGHT])
(;W[re];B[oa];W[rd];B[na]C[RIGHT])))
(;W[rc];B[rd];W[re];B[sc];W[se];B[sd]C[RIGHT])
(;W[sc];B[sd];W[rd];B[rc];W[re];B[ob]C[RIGHT])
(;W[sd];B[rc];W[rd];B[re];W[rf];B[ob]C[RIGHT])
(;W[re];B[rc];W[rd];B[ob]C[RIGHT])
(;W[se]C[You descended to the first line and so did White. Strange, innocent? Guess you will find out pretty soon :)CHOICE]
(;B[rc];W[rd]
(;B[qa];W[pa]
(;B[ob];W[sc]
(;B[sd]C[Ko, Black takes first.RIGHT])
(;B[oa];W[sa])
(;B[re];W[sa]))
(;B[oa];W[ob]
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[na]
(;B[sd];W[sc]C[Ko, White takes first])
(;B[ma];W[sc]
(;B[oa];W[sa])
(;B[sd]C[Ko, Black takes first.RIGHT]))
(;B[sa];W[sc])
(;B[sc];W[sd])
(;B[re];W[rf];B[ma];W[sc];B[sd]C[Yeah, right.RIGHT]))
(;B[re];W[rf];B[nb];W[na])
(;B[na];W[nb]))
(;B[sc];W[sd])
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[re];W[rf]
(;B[ob];W[sc];B[sd]C[RIGHT])
(;B[oa];W[sc];B[sd]C[RIGHT])
(;B[sd];W[sc]C[Ko, White takes first.]))
(;B[sa];W[sc]))
(;B[pa];W[ob]
(;B[nb];W[oa])
(;B[qa];W[oa]
(;B[qa];W[sd])
(;B[sd];W[re]
(;B[qa];W[sc]C[Ko, White takes first.])
(;B[nb];W[qa])
(;B[na];W[qa]))
(;B[nb];W[qa])
(;B[na];W[qa]))
(;B[oa];W[nb])
(;B[sd];W[re]
(;B[nb];W[oa])
(;B[qa];W[oa])
(;B[oa];W[nb])))
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[re];W[rf]
(;B[ob];W[sc]
(;B[sd]C[Ko, Black takes first.RIGHT])
(;B[pa];W[sa])
(;B[qa];W[sa]))
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[qa];W[pa])
(;B[pa];W[ob]
(;B[qa];W[oa]
(;B[qa];W[sd])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[qa])
(;B[na];W[qa])
(;B[sa];W[sc]))
(;B[sa];W[sc])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[oa])
(;B[oa];W[nb])))
(;B[ob];W[sc];B[sd]C[Ko, Black takes first.RIGHT]))
(;B[ob];W[rc]
(;B[pa];W[rd])
(;B[qa];W[rd])
(;B[rd];W[re]
(;B[sc];W[sd])
(;B[pa];W[sd])
(;B[sd];W[sc]))
(;B[re];W[rd])
(;B[sc];W[rd])
(;B[sd];W[rd]))
(;B[rd];W[sd]
(;B[ob];W[re])
(;B[re];W[rf]
(;B[rc];W[sf])
(;B[ob];W[rc])
(;B[sc];W[rc])
(;B[sf];W[rc]))
(;B[rc];W[re])
(;B[sc];W[re]))
(;B[sd];W[rd]
(;B[rc];W[sc]C[Ko, White takes first.])
(;B[ob];W[rc])
(;B[sc];W[rc]))
(;B[re];W[rf]
(;B[sd];W[rc]
(;B[rd];W[sc])
(;B[sf];W[rd])
(;B[sc];W[rd])
(;B[ob];W[rd]))
(;B[rc];W[rd]
(;B[ob];W[sc]
(;B[sd]C[Ko, Black takes first.RIGHT])
(;B[pa];W[sa])
(;B[qa];W[sa]))
(;B[sd];W[sc]C[Ko, White takes first.])
(;B[qa];W[pa])
(;B[pa];W[ob]
(;B[qa];W[oa]
(;B[qa];W[sd])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[qa])
(;B[na];W[qa])
(;B[sa];W[sc]))
(;B[sa];W[sc])
(;B[sd];W[sc]C[Ko, White takes first])
(;B[nb];W[oa])
(;B[oa];W[nb])))
(;B[rd];W[sd]
(;B[rc];W[sf])
(;B[ob];W[rc])
(;B[sc];W[rc])
(;B[sf];W[rc]))
(;B[sc];W[rd])
(;B[ob];W[rc])
(;B[sf];W[rc])
(;B[qa];W[rc]))
(;B[sc];W[rd])
(;B[qa];W[rc];B[rd];W[sd];B[sc];W[re])))
(;B[rc];W[sb]
(;B[sc];W[sd]
(;B[sa];W[qa]
(;B[se];W[sb]C[Ko, White takes first])
(;B[ob];W[sb]C[Ko, White takes first])
(;B[rd];W[re]
(;B[se];W[sb]C[Ko, White takes first])
(;B[ob];W[sb]))
(;B[re];W[rf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[rd];W[sf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[se];W[sb]C[Ko, White takes first.])
(;B[sb];W[se]))
(;B[sb];W[rd])
(;B[se];W[sf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[rd];W[sb]C[Ko, White takes first.]))))
(;B[rd];W[re])
(;B[re];W[rd])
(;B[ob];W[rd])
(;B[se];W[rd])
(;B[qa];W[rd]))
(;B[re];W[sc];B[rd];W[rf])
(;B[ob];W[rd])
(;B[sd];W[re]
(;B[sc];W[rd];B[sa];W[qa];B[ob];W[sb]C[Ko, White takes first.])
(;B[ob];W[rd])
(;B[rd];W[se]))
(;B[rd];W[re])
(;B[se];W[rd])
(;B[qa];W[pa]
(;B[sc];W[sd];B[sa];W[qa]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[rd];W[re]
(;B[se];W[sb]C[Ko, White takes first.])
(;B[ob];W[sb])
(;B[oa];W[sb]))
(;B[oa];W[sb]C[Ko, White takes first.])
(;B[re];W[rf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[oa];W[sb]C[Ko, White takes first.])
(;B[rd];W[sf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[se];W[sb]C[Ko, White takes first.])
(;B[oa];W[sb]C[Ko, White takes first.]))
(;B[se];W[sf]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[oa];W[sb]C[Ko, White takes first.])
(;B[rd];W[sb]C[Ko, White takes first.])))
(;B[se];W[re]
(;B[rd];W[sb]C[Ko, White takes first.])
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[oa];W[sb]C[Ko, White takes first.])))
(;B[ob];W[rd])
(;B[oa];W[rd])
(;B[sd];W[re]
(;B[sc];W[rd];B[sa];W[qa]
(;B[ob];W[sb]C[Ko, White takes first.])
(;B[oa];W[sb]C[Ko, White takes first.]))
(;B[ob];W[rd])
(;B[oa];W[rd]))
(;B[rd];W[re])
(;B[re];W[sc];B[rd];W[rf])
(;B[se];W[rd])))
(;B[sc];W[rd])
(;B[rd]
(;W[sb]
(;B[sc];W[rc]C[Ko, White takes first.])
(;B[rc];W[re])
(;B[sd];W[rc])
(;B[re];W[rc]C[Whiote could also play S14 for a favourable ko.])
(;B[se];W[rc])
(;B[ob];W[rc]))
(;W[re]C[In general S15 will be a better defense for White than T18, but it may depend on the situation on the rest of the board.]
(;B[sc];W[se]
(;B[sd];W[sb]
(;B[sa];W[qa];B[ob];W[sb]C[Ko, White takes first.])
(;B[ob];W[rc])
(;B[qa];W[rc]))
(;B[ob];W[sd])
(;B[qa];W[sd])
(;B[sb];W[sd]))
(;B[sd];W[sb]
(;B[sc];W[rc]C[Ko, White takes first.])
(;B[se];W[rg])
(;B[ob];W[rc])
(;B[qa];W[rc]))
(;B[sb];W[sd])
(;B[se];W[sf]
(;B[sc];W[sd]MA[sb]C[Dead in double ko. If Black retakes at T15 White will play T18.])
(;B[sd];W[sc])
(;B[rc];W[sd])
(;B[sb];W[sd]
(;B[rc];W[se])
(;B[ob];W[rc]))
(;B[ob];W[sd])
(;B[qa];W[sd]
(;B[rc];W[pa]
(;B[sb];W[se])
(;B[ob];W[sb]))
(;B[sa];W[rc])
(;B[sc];W[rc])
(;B[ob];W[rc]))
(;B[rf];W[sd]))
(;B[rc];W[sb])
(;B[sa];W[sd]
(;B[qa];W[rc])
(;B[sc];W[rc])
(;B[rc];W[sb])
(;B[ob];W[rc]))
(;B[ob];W[sd])
(;B[qa];W[sd]
(;B[rc];W[pa]
(;B[sb];W[se])
(;B[ob];W[sb]))
(;B[sa];W[rc])
(;B[ob];W[rc])
(;B[sc];W[rc]))))
(;B[re];W[sb]
(;B[rf];W[rd])
(;B[rd];W[rc]C[Whiote could also play S14 for a favourable ko.])
(;B[rc];W[sc];B[rd];W[rf])
(;B[sc];W[rd])
(;B[sd];W[rc])
(;B[se];W[rd]))
(;B[sd]
(;W[rc];B[rd];W[sb]C[White lives (Thanks to Bass)])
(;W[sb];B[rc];W[re]
(;B[sc];W[rd];B[sa];W[qa];B[ob];W[sb]C[Ko, White takes first.])
(;B[ob];W[rd])
(;B[rd];W[se]))
(;W[rd];B[rc];W[re];B[sb];W[se];B[ob];W[sc]))
(;B[se];W[rd])
(;B[ob];W[rd])
(;B[qa];W[rc]
(;B[rd];W[sb])
(;B[sa];W[rd])
(;B[ob];W[sb]))
(;B[pa];W[rd])
(;B[sa];W[rc]))
