Black to play - How can black kill the white stones
(;AP[goproblems]AB[qa]AB[qb]AB[qc]AB[pc]AB[oc]AB[nd]AB[md]AB[lc]AB[kc]AB[jc]AB[jb]AB[ja]AW[ka]AW[kb]AW[lb]AW[mb]AW[mc]AW[ma]AW[nc]AW[ob]AW[pb]C[If White plays now, he can guarantee himself 2 eyes.](;B[oa];W[pa](;B[nb]C[RIGHT])(;B[na];W[nb]))(;B[pa];W[oa])(;B[na];W[nb](;B[pa];W[oa])(;B[oa];W[pa]))(;B[nb];W[na](;B[pa];W[oa])(;B[oa];W[pa])))