(;AB[qa]AB[qb]AB[qc]AB[pd]AB[pe]AB[qf]AB[pf]AB[pg]AW[qe]AW[qd]AW[rc]AW[rb]AW[ra]AB[se]TR[se]LB[oc:No]C[White's corner is in danger, but Black's stone at T15 looks a bit awkward. Can White save the corner? Play P17 ('No') if you think not.FORCE]AP[goproblems] (;W[oc]AW[qa]AW[qb]AW[qc]AW[pd]AW[pe]AW[qf]AW[pf]AW[pg]AB[qe]AB[qd]AB[rc]AB[rb]AB[ra]AW[se]C[];B[rf]C[You thought the corner was dead. So the stones have been swapped and Black has just played S14. Can you kill the corner?] (;W[rg];B[sd] (;W[sf] (;B[sb] (;W[rd]C[RIGHT]) (;W[re];B[rd])) (;B[sg]C[CHOICE] (;W[sh];B[sb] (;W[rd]C[RIGHT]) (;W[re];B[rd])) (;W[re];B[rd] (;W[sb];B[rf]) (;W[sh];B[sb]) (;W[rf];B[sb])) (;W[rd];B[re]) (;W[sb];B[re]) (;W[sc];B[re]))) (;W[re];B[rd] (;W[sb];B[sf]) (;W[sf];B[sb])) (;W[rd];B[re]) (;W[sg];B[sb] (;W[rd];B[re];W[sf];B[rd]) (;W[re];B[rd]) (;W[sf];B[rd])) (;W[sb];B[sf]) (;W[sc];B[sb] (;W[sf];B[rd]) (;W[rd];B[re]) (;W[re];B[rd]))) (;W[re];B[rd] (;W[rg];B[sd] (;W[sf];B[sb]) (;W[sb];B[sf])) (;W[sd];B[rg]C[The corner lives and grows rapidly.]) (;W[sb];B[rg]C[The corner lives and grows like cabbage.]) (;W[sf];B[rg]C[Come on...!]) (;W[sc];B[rg]C[Alive and kicking.])) (;W[rd];B[re] (;W[rg];B[sd]) (;W[sd];B[rg]C[Black gains some extra points.]) (;W[sc];B[sf] (;W[sb];B[sd]) (;W[rg];B[sd]) (;W[sd]C[Black plays elsewhere, satisfied with living in sente.])) (;W[sf];B[rg]) (;W[sb];B[sd])) (;W[sf];B[rg]C[This only helps Black.]) (;W[sd];B[rg]C[Black's corner grows rapidly.]) (;W[sg];B[rg] (;W[rh];B[re] (;W[sf];B[sd] (;W[sh];B[sb]) (;W[qg];B[sh])) (;W[qg];B[sd] (;W[sf];B[sh]) (;W[sh];B[sf])) (;W[sd];B[sf]) (;W[rd];B[sd])) (;W[sf];B[sd] (;W[re];B[rd]MA[sh]MA[sb]C[Either way Black lives.]) (;W[rd];B[re]MA[sh]MA[sb]C[Black lives.]) (;W[sb];B[sh])) (;W[re];B[rd] (;W[rh];B[sd]) (;W[sf];B[rh]) (;W[qg];B[rh])) (;W[rd];B[re])) (;W[sb];B[sd] (;W[re];B[rd]) (;W[rg];B[re]) (;W[sf];B[rg]) (;W[sg];B[rg]) (;W[rd];B[re])) (;W[sc];B[rd] (;W[sd];B[rg]) (;W[rg];B[sf]) (;W[re];B[rg]) (;W[sf];B[rg]) (;W[sb];B[rg]) (;W[sg];B[rg]))) (;W[rf];B[rg] (;W[sf];B[rd]C[White cannot live without the marked stones; and they remain in atari even if White connects.]TR[qe]TR[qd]) (;W[sd];B[sf] (;W[re];B[rd]) (;W[sb];B[rd] (;W[re];B[rd]) (;W[sg];B[re])) (;W[rd];B[sb]) (;W[sg];B[sh] (;W[sb];B[rd];W[re];B[rd]) (;W[re];B[rd]) (;W[rd];B[sb])) (;W[pc];B[rd] (;W[pb];B[re]) (;W[re];B[rd]) (;W[sg];B[re]) (;W[pa];B[re]))) (;W[re];B[sf] (;W[sd];B[rd]) (;W[rd]C[White dies in gote.]) (;W[sb]C[White remains dead even without Black playing.])) (;W[rd];B[sf] (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[re]C[White is dead even if Black plays elsewhere.]) (;W[pc];B[pb] (;W[oc];B[ob]C[Black can keep on crawling until Black has enough liberties to kill the corner.White can't block; Black would cut.]) (;W[re]C[White is dead as it stands.]) (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[sg];B[sh] (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[re]C[White is dead as it stands.]) (;W[oc];B[ob]C[Black can keep on crawling until Black has enough liberties to kill the corner.White can't block; Black would cut.]))) (;W[sg];B[sh] (;W[pc];B[pb] (;W[oc];B[ob]C[Black can keep on crawling until Black has enough liberties to kill the corner.White can't block; Black would cut.]) (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[re]C[White is dead...!])) (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[re]C[White is dead as it stands.]))) (;W[sb];B[rd]) (;W[sg];B[rd]) (;W[pc];B[rd])) (;W[re];B[rf] (;W[sd];B[rd]) (;W[rd]C[White dies even if Black plays elsewhere.]) (;W[sb]C[White has only one eye, because Black can play either at S16 or at T16.]) (;W[sf];B[rd])) (;W[rd];B[rf] (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[pc];B[pb] (;W[sd];B[sb]) (;W[sb];B[sd]) (;W[oc];B[ob]C[Black can keep on crawling until Black has enough liberties to kill the corner.White can't block; Black would cut.]))) (;W[sd];B[rf] (;W[rd];B[sb]) (;W[sb];B[rd] (;W[re];B[rd]) (;W[sf];B[re])) (;W[re];B[rd]) (;W[sf];B[re] (;W[rd];B[sb]) (;W[sb];B[rd])) (;W[pc];B[rd] (;W[pb];B[re]) (;W[re];B[rd]) (;W[sf];B[re]))) (;W[sf];B[rd]) (;W[sb];B[rd]) (;W[sc];B[rd]) (;W[rg];B[rd]) (;W[sg];B[rd]) (;W[pc];B[rd]))