(;AB[rb]AB[rc]AB[sc]AB[re]AB[qe]AB[pe]AB[od]AB[nc]AB[nb]AW[sd]AW[rd]AW[qd]AW[qc]AW[pc]AW[pb]AW[pa]C[Kill the white stones. No Seki or Ko.]AP[goproblems]
(;B[sb]
(;W[qb]
(;B[ra]C[White is dead. If white captures the black killing shape, black plays at S18 which creates a dead eye space.RIGHT]MA[ra]MA[sb]MA[sc]MA[rc]TR[rb])
(;B[sa];W[ra]C[White lives.])
(;B[se];W[ra]C[White lives. The black stones are a killing shape, but without the required single shared liberty.]))
(;W[ra]
(;B[qb]C[White is dead. If white captures the black killing shape, black plays at S18 which creates a dead eye space.RIGHT]TR[rb]MA[qb]MA[sb]MA[sc]MA[rc])
(;B[sa];W[qb]C[White lives.])
(;B[se];W[qb]C[White lives. The black stones are a killing shape, but without the required single shared liberty.])))
(;B[sa]
(;W[qb]C[White lives. Black T18 would create a killing shape, but without the required single shared liberty.]))
(;B[qb];W[sb]
(;B[sa];W[qa]C[White lives.])
(;B[qa];W[ra]C[White lives.])
(;B[ra]C[White lives.]))
(;B[qa];W[qb]C[White lives. No ko.]MA[sa];B[sa]C[No Ko.NOTTHIS])
(;B[ra];W[sb]C[White lives.]))