(;AB[ka]AB[kb]AB[jb]AB[ib]AB[jc]AB[jd]AB[je]AB[ie]AB[ke]AB[le]AB[lc]SZ[12]AW[he]AW[id]AW[ic]AW[hb]AW[ja]AW[ia]AW[ha]AW[ga]AW[gb]AW[gc]AW[gd]AW[fc]AW[fe]AW[ee]AW[df]AW[cf]AW[bf]AW[ce]AW[cd]AB[de]AB[dd]AB[ed]AB[fd]AB[ec]AB[fb]AB[fa]AB[cc]AB[bc]AB[bd]AB[be]AB[bb]AB[db]AB[ae]AW[kf]AB[hf]AB[if]AB[jf]AW[gf]AW[lg]AW[jg]AW[kh]AW[ig]AW[hg]AB[gg]C[Black plays the triangle stone, and white responds with squared one. Show his mistake!]AW[gh]AB[fg]AW[eh]MA[eh]TR[fg]AW[bh]AW[bg]AW[bi]AW[bj]AW[gi]AW[gj]AW[jj]AW[ii]AW[dk]AW[ck]AB[fh]AB[ei]AB[fi]AP[goproblems] (;B[hd];W[ef] (;B[ff];W[ge];B[hc]) (;B[hc];W[ge])) (;B[eg]) (;B[ff];W[ef]C[];B[ge]C[Black starts a ko but lacks ko threats. Black can win the game without ko. (see variations)]) (;B[ef];W[eg];B[ff]C[RIGHT]))