In this common 3-3 invasion, black played 15, and white played elsewhere. Can black get anything else out of the corner?
(;AB[na]AB[nb]AB[oc]AB[od]AB[pd]AB[qd]AB[re]AB[sd]AW[rd]AW[rc]AW[qc]AW[qb]AW[pc]AW[ob]AW[oa]LB[pd:1]LB[qc:2]LB[qd:3]LB[pc:4]LB[oc:5]LB[rd:6]LB[re:7]LB[rc:8]LB[od:9]LB[ob:10]LB[nb:11]LB[oa:12]LB[na:13]LB[qb:14]LB[sd:15]C[Black to do something in the corner]AP[goproblems]
(;B[rb];W[sb]
(;B[ra];W[qa];B[pa];W[pb])
(;B[pa]C[]
(;W[ra];B[pb])
(;W[pb];B[ra];W[qa]))
(;B[qa];W[ra]))
(;B[ra];W[qa]
(;B[pb];W[pa];B[sb];W[sc];B[se]C[Seki, but you lost one point from the capture.])
(;B[sb]C[];W[sc]
(;B[pb]
(;W[pa];B[se]C[Seki, but you lost one point from the capture.])
(;W[rf]C[White escapesCHOICE]))
(;B[pa]C[RIGHT]
(;W[pb]C[Seki, but you lost one point from the capture.];B[se]C[Seki, but you lost one point from the capture.])
(;W[rf]C[White escapesCHOICE]))
(;B[se]C[Seki - if white forces life at S18, black will capture two stones, resulting in a net of zero points in the corner for both players. Best result.CHOICERIGHT]))
(;B[sc];W[sb])
(;B[pa];W[pb];B[sb];W[sc];B[se]C[Seki, but you lost one point from the capture.]))
(;B[qa];W[ra]
(;B[sb];W[sc])
(;B[sc];W[sb];B[pa];W[se]
(;B[pb])
(;B[sd];W[sc]))
(;B[pa];W[pb])
(;B[pb];W[pa]))
(;B[sc];W[sb]
(;B[pa];W[ra];B[pb];W[se])
(;B[qa];W[ra];B[pa];W[se]
(;B[pb])
(;B[sd];W[sc]))
(;B[ra];W[qa]))
(;B[pa];W[pb]
(;B[ra];W[qa];B[sb];W[sc]C[Seki, but you lost one point from the capture.];B[se]C[Seki, but you lost one point from the capture.])
(;B[sb];W[sc];B[ra]
(;W[qa]C[Seki];B[se]C[Seki, but you lost one point from the capture.])
(;W[se]C[CHOICE]))
(;B[rb];W[sb];B[ra];W[qa])
(;B[sc];W[sb];B[ra];W[qa])
(;B[qa];W[ra]))
(;B[pb];W[pa];B[sb];W[ra];B[sc];W[rb])
(;B[se];W[sb]))