(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2] RU[Japanese]SZ[19]KM[6.50] PW[White]PB[Black]AW[oa][pa][ob][oc][pd][pe][of][qf][qg][rg][qh][qi][ri][rj][sj]AB[qa][pb][rb][pc][qd][qe][re][rf][sf][sg][rh][sh][si]LB[mh:S]C[Does Black need to defend or is his group unconditionally alive and making points? Play S if it is safe. Otherwise, play a defensive move.] (;B[mh] ;W[rc]C[Then prove it.] (;B[qc] ;W[sb] (;B[sd] ;W[ra] (;B[qb] ;W[sc] (;B[sa]C[So there is a ko.]) (;B[rd] ;W[se])) (;B[sc] ;W[qb])) (;B[sc] ;W[sd] ;B[rd] ;W[ra] (;B[qb] ;W[se]) (;B[sc] ;W[qb]C[Ko.])) (;B[sa] ;W[ra] ;B[qb] ;W[sd] (;B[rd] ;W[se]) (;B[sa] ;W[sc]C[A very difficult ko for Black.])) (;B[rd] ;W[ra] (;B[sc] ;W[qb]C[Ko.]) (;B[qb] ;W[sc] (;B[sd] ;W[se]) (;B[sa]C[So there is a ko.]))) (;B[ra] ;W[sd] ;B[rd] ;W[sc]C[Seki.]) (;B[se] ;W[ra] (;B[qb] ;W[sd] ;B[sa]C[So there is a ko.]) (;B[rd] ;W[qb]) (;B[sc] ;W[qb]) (;B[sd] ;W[qb]) (;B[sa]C[So there is a ko.])) (;B[qb] ;W[sd] (;B[rd] ;W[sc] (;B[ra]C[Seki.]) (;B[sa] ;W[ra]C[Ko.])) (;B[ra] ;W[sc]C[Seki.]) (;B[sa] ;W[ra]C[There is a ko.] (;B[rd] ;W[se]) (;B[se] ;W[rd])) (;B[se] ;W[sc] (;B[rd] ;W[ra]) (;B[sa] ;W[ra]C[A very difficult ko for Black.])))) (;B[sb] ;W[qc] ;B[qb] ;W[rd]) (;B[qb] ;W[sb] (;B[qc] ;W[sd] (;B[rd] ;W[sc] (;B[ra]C[Seki.]) (;B[sa] ;W[ra]C[Ko.])) (;B[ra] ;W[sc]C[Seki.])) (;B[sc] ;W[sd] ;B[rd] ;W[ra]C[Ko.]) (;B[sd] ;W[qc]) (;B[rd] ;W[sd] ;B[qc] ;W[sc] (;B[sa] ;W[ra]C[Ko.]) (;B[se] ;W[ra]) (;B[ra]C[So there is a seki.])) (;B[sa] ;W[ra] ;B[qc] ;W[rd] ;B[sa]C[So there is a ko.])) (;B[rd] ;W[sb] (;B[qc] ;W[sd] (;B[sa] ;W[ra] ;B[qb] ;W[sc] ;B[sa]C[So there is a ko.]) (;B[sc]C[So there is a ko.])) (;B[sa] ;W[qc]) (;B[qb] ;W[sd] ;B[sa] ;W[sc]C[Black cannot avoid the ko.] (;B[ra] ;W[qc]) (;B[se] ;W[qc]) (;B[qc] ;W[ra]C[Ko.])) (;B[ra] ;W[qc]) (;B[sd] ;W[qc]) (;B[sc] ;W[sd] ;B[qc] ;W[sc] (;B[se] ;W[qb]) (;B[ra]C[So there is a seki.]) (;B[sa] ;W[ra]C[Ko.]))) (;B[ra] ;W[qc] ;B[qb] ;W[rd]) (;B[sa] ;W[qc] ;B[qb] ;W[rd]) (;B[se] ;W[qc] ;B[qb] ;W[sd]) (;B[sd] ;W[qc] ;B[qb] ;W[sb]) (;B[sc] ;W[sb] (;B[sa] ;W[sd] (;B[rd] ;W[sb] (;B[qc] ;W[ra]C[Ko.]) (;B[se] ;W[qc]) (;B[ra] ;W[qb]) (;B[qb]C[Ko.] ;W[ra])) (;B[se] ;W[qc]) (;B[sb] ;W[qc]) (;B[ra] ;W[qc]) (;B[qc] ;W[sb] (;B[ra] ;W[qb]) (;B[qb] ;W[ra]C[Ko.]) (;B[rd] ;W[ra]C[Ko.]) (;B[se] ;W[ra]C[Ko.])) (;B[qb] ;W[sb]C[Black cannot avoid a ko.] (;B[rd] ;W[ra]C[Ko.]) (;B[se] ;W[qc]) (;B[ra] ;W[qc]) (;B[qc] ;W[ra]C[Ko.]))) (;B[ra] ;W[qc]) (;B[qb] ;W[sd] (;B[rd] ;W[sc] ;B[sa] ;W[ra]C[Ko.]) (;B[qc] ;W[ra]C[Ko.]) (;B[se] ;W[qc]) (;B[ra] ;W[qc]) (;B[sa] ;W[ra]C[Ko.])) (;B[qc] ;W[sd] (;B[rd] ;W[sc] (;B[ra]C[Seki.]) (;B[sa] ;W[ra]C[Ko.]) (;B[se] ;W[qb])) (;B[ra] ;W[sc]C[Seki.]) (;B[sa] ;W[ra]C[Black cannot avoid the ko.] ;B[qb] ;W[se] ;B[sa]C[Ko.]) (;B[se] ;W[ra]C[Ko.]) (;B[qb] ;W[ra]C[Ko.])) (;B[rd] ;W[sd] (;B[se] ;W[qc]) (;B[qc] ;W[sc] (;B[sa] ;W[ra]C[Ko.]) (;B[ra]C[Seki.]) (;B[qb] ;W[ra]C[Ko.])) (;B[qb] ;W[ra]C[Ko.]) (;B[ra] ;W[qc]) (;B[sa] ;W[qc] (;B[sc] ;W[qb]) (;B[qb] ;W[ra]) (;B[ra] ;W[qb]))) (;B[sd] ;W[qc]) (;B[se] ;W[qc]))) (;B[rc]C[RIGHT There was a weak point!]) (;B[qc]C[RIGHT There was a weak point!]) (;B[qb]C[RIGHT There was a weak point!]) (;B[sb]C[RIGHT There was a weak point!]) (;B[rd]C[RIGHT There was a weak point!]) (;B[sc]C[RIGHT There was a weak point!]) (;B[sd]C[RIGHT There was a weak point!]) (;B[ra] ;W[rc] (;B[sc] ;W[sd] (;B[sb] ;W[qc]) (;B[qc] ;W[sb] ;B[rd] ;W[sc]C[Seki.]) (;B[rd] ;W[sb] (;B[sa] ;W[qb]) (;B[se] ;W[qc]) (;B[qc] ;W[sc]C[Seki.]))) (;B[qb] ;W[sb] (;B[sc] ;W[sd] (;B[qc] ;W[sc]C[Seki]) (;B[rd] ;W[sc] (;B[qc]C[Seki.]) (;B[se] ;W[qc]) (;B[sa] ;W[qc])) (;B[se] ;W[qc]) (;B[sa] ;W[qc])) (;B[sd] ;W[qc]) (;B[se] ;W[qc]) (;B[sa] ;W[qc]) (;B[rd] ;W[sd] (;B[sa] ;W[qc]) (;B[se] ;W[qc]) (;B[qc] ;W[sc]C[Seki.])) (;B[qc] ;W[sd]C[Seki.])) (;B[qc] ;W[sb] (;B[rd] ;W[sd] ;B[sc]C[Ko. If White wins the ko, it's a seki.]) (;B[sc] ;W[sd] ;B[rd] ;W[sc]C[Seki.]) (;B[sd]C[RIGHT])) (;B[sd] ;W[qc] ;B[qb] ;W[sb]) (;B[rd] ;W[sb] (;B[sd] ;W[qc]) (;B[sc] ;W[sd] ;B[qc] ;W[sc]C[Seki.]) (;B[qc] ;W[sd] ;B[sc]C[Ko. If White wins the ko, it's a seki.]))) (;B[sa] ;W[rc] (;B[qb] ;W[sd] (;B[sb] ;W[qc] (;B[sc] ;W[ra]) (;B[rd] ;W[se]) (;B[se] ;W[rd])) (;B[qc] ;W[sb] (;B[rd] ;W[ra] ;B[sc]C[RIGHT You chose the most complicated way of defending, though.]) (;B[se] ;W[ra]C[Ko.]) (;B[ra] ;W[sc]C[Black is dead.])) (;B[sc] ;W[sb]C[Ko.]) (;B[se] ;W[qc]) (;B[rd] ;W[sb] (;B[qc] ;W[ra] ;B[sc]C[RIGHT You chose the most complicated way to defend, though.]) (;B[ra] ;W[qc]) (;B[se] ;W[qc]))) (;B[qc] ;W[sd] ;B[sc] ;W[sb] ;B[rd] ;W[ra]C[Ko. If Black captures at T17, White captures at R18 (Black connecting at R18 is self-atari).]) (;B[sb] ;W[qc] ;B[qb] ;W[rd]) (;B[ra] ;W[qc]) (;B[sd] ;W[qc] ;B[qb] ;W[sc]C[Seki.]) (;B[se] ;W[qc] ;B[qb] ;W[sd]) (;B[rd] ;W[qc] ;B[qb] ;W[sc]C[Seki.]) (;B[sc] ;W[sd] (;B[sb] ;W[qc] ;B[qb] ;W[ra]) (;B[rd] ;W[sb] ;B[qc] ;W[ra]C[Ko.]) (;B[qc] ;W[sb]C[Ko.] (;B[ra] ;W[qb]) (;B[rd] ;W[ra])) (;B[qb] ;W[sb]C[Ko.]) (;B[se] ;W[qc] (;B[qb] ;W[rd]) (;B[rd] ;W[sd])) (;B[ra] ;W[qc] (;B[rd] ;W[se]) (;B[qb] ;W[sb])))) (;B[se] ;W[rc] (;B[qb] ;W[sb] (;B[qc] ;W[sd] (;B[sa] ;W[ra]C[Ko.]) (;B[ra] ;W[sc]C[Black is dead.]) (;B[rd] ;W[ra])) (;B[sc] ;W[sd] ;B[qc] ;W[sc] ;B[sa] ;W[ra]C[Ko.]) (;B[sd] ;W[qc]) (;B[rd] ;W[ra]C[Ko.]) (;B[ra] ;W[qc])) (;B[qc] ;W[sb] (;B[sa] ;W[ra] ;B[qb] ;W[sd] ;B[sa]C[Ko.]) (;B[sc] ;W[sd] (;B[ra] ;W[sc]C[Seki.]) (;B[sa] ;W[ra]C[Ko.]))) (;B[ra] ;W[qc] ;B[qb] ;W[sd]) (;B[rd] ;W[qc] ;B[qb] ;W[sd]) (;B[sa] ;W[qc] ;B[qb] ;W[sd]) (;B[sb] ;W[qc] ;B[qb] ;W[sd]) (;B[sd] ;W[qc] ;B[qb] ;W[sc]) (;B[sc] ;W[sb] (;B[sd] ;W[qc]) (;B[qc] ;W[sd] (;B[ra] ;W[sc]C[Seki.]) (;B[sa] ;W[ra]C[Ko.])) (;B[sa]C[RIGHT You chose a very complicated way to defend, though.]))))