(;AB[rc]AB[qc]AB[qb]AB[qd]AB[pd]AB[od]AB[nc]AW[oc]AW[pc]AW[pb]AW[oa]AW[nb]AW[lc]AW[md]AW[ne]AW[oe]AW[pe]AW[qe]AW[re]AW[rd]C[Black to play. Black wants to live in the corner, either outright or by fighting a ko. How should he play?]SZ[19]CA[utf-8]RU[Japanese]GM[1]FF[4]AP[CGoban:3]ST[2]PB[Musta]PW[Valkea]KM[0]MULTIGOGM[1] (;B[pa];W[qa];B[ra];W[sb];B[pa]C[RIGHT]C[CORRECTRIGHT]) (;B[ra];W[sb];B[pa];W[qa]TR[ob]C[White takes the ko first, so this is bad for Black. White also has an extra adjacent ko-threat at the marked point.]) (;B[qa];W[pa] (;B[sb];W[ra]) (;B[ra];W[sb];B[mb];W[mc];B[nd];W[lb];B[ma];W[la])) (;B[mb];W[nd] (;B[pa];W[qa];B[ra];W[sb];B[pa];W[mc]) (;B[ra];W[sb]) (;B[mc];W[lb]) (;B[qa];W[sb]) (;B[ma];W[mc])) (;B[sb];W[ra]))