This is something that beginners seem to get caught by.
Correct response to w1 is B13
(;AB[bh]AB[ch]AW[bi]AW[ci]AW[di]AW[dh]AB[dg]AB[df]AB[de]AW[eh]AW[ff]AB[be]AB[ag]AW[ah]AW[bk]LB[ah:1]LB[ag:2]C[Punish black's mistake]AB[dd]AP[goproblems]
(;W[bg]
(;B[ai]C[CHOICE]
(;W[cg];B[ah]
(;W[af];B[aj]
(;W[bj]C[RIGHT])
(;W[ak]C[RIGHT]))
(;W[aj];B[af]C[Black escapes]))
(;W[af];B[cg];W[ah]C[Ko, White can do much better])
(;W[aj];B[cg];W[ah]C[Ko, white can do better]))
(;B[cg];W[af]C[Probably the best choice for black.])
(;B[af];W[cg]))
(;W[ai]
(;B[bf]C[White can do much betterCHOICE])
(;B[bg]C[White can do much betterCHOICE])
(;B[cg]C[White can do much betterCHOICE]))
(;W[cg];B[bg]
(;W[bf];B[cf])
(;W[cf];B[bf]))
(;W[af];B[bg]
(;W[bf]
(;B[cg])
(;B[ai];W[aj];B[cg]))
(;W[cg];B[cf])
(;W[cf]
(;B[bf])
(;B[cg])))
(;W[bf];B[bg]
(;W[af];B[cg])
(;W[cg];B[cf])
(;W[cf];B[cg]))
(;W[cf]
(;B[bg];W[cg];B[bf])
(;B[cg]
(;W[af];B[ai])
(;W[bf]
(;B[af])
(;B[ai]C[CHOICE])))
(;B[bf];W[bg];B[ai]
(;W[cg];B[ce])
(;W[aj];B[ah];W[cg];B[ce])))
(;W[aa]C[Now don't be silly :D])
(;W[ce];B[bf])
(;W[ae];B[bf]))