Due to the rather large amount of possible correct variations, i've likely missed some. Should be more than enough, though.
(;AB[ja]AB[jc]AB[kb]AB[ka]AB[lb]AB[la]AB[kc]AB[ld]AB[kd]AB[jd]AB[id]AB[ke]AB[ie]AB[if]AB[jf]AB[hf]AB[gf]AB[ge]AB[gd]AB[fd]AB[fc]AB[ee]AB[de]AB[dd]AB[df]AB[dg]AB[dh]AB[cf]AB[hh]AW[kf]AW[kg]AW[jg]AW[ig]AW[jh]AW[lh]AW[le]AW[me]AW[md]AW[fe]AW[ia]AW[jb]AW[ic]AW[hb]AW[hc]AW[hd]AW[he]AW[gc]AW[fb]AW[ec]AW[dc]AW[ed]AW[cd]AW[ce]AW[bf]AW[cg]AW[bg]AW[ch]AB[hg]AW[mb]AW[ma]AW[mc]AW[ib]C[White has made the mistake of answering the endgame move K17 with J18. Black to punish white.]AB[be]LB[jc:1]LB[ib:2]AP[goproblems]
(;B[ha];W[ga]C[That acomplishes nothing.])
(;B[gb];W[ga]C[That acomplishes nothing.])
(;B[bd];W[cc]C[Nothing more for black to do here.])
(;B[cc]
(;W[bd]
(;B[bc];W[ae]
(;B[db];W[eb]
(;B[ga];W[gb]
(;B[da];W[bb]
(;B[cb];W[ac]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[fa]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[ca];W[ba])
(;B[ba];W[ab]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[fa]C[Correct. In this sequence, white can make a ko for B19.])))
(;B[ab];W[cb];B[ac];W[ad])
(;B[ac];W[cb])
(;B[ea];W[cb])
(;B[fa];W[cb]))
(;B[ea];W[cb]C[White lives.])
(;B[ca];W[ac]
(;B[bb];W[ab]
(;B[ea];W[ba];B[aa]MA[ba]C[Ko. This is bad.])
(;B[da];W[ba];B[aa]MA[ba]C[Ko. This is bad.])
(;B[ba];W[ea]
(;B[fa]C[Black wins the semeai without ko. Thanks to sestir for this solution!RIGHT];W[ad];B[da])
(;B[aa];W[ad]
(;B[fa]C[Seki])
(;B[ha]C[Seki.]))
(;B[da]C[Black wins the semeai without ko. Thanks to sestir for this solution!RIGHT])
(;B[ha]C[Black wins the semeai without ko. Thanks to sestir for this solution!RIGHT]))
(;B[aa];W[ba]C[Ko.]))
(;B[cb];W[ea]C[Black will not be able to approach.])
(;B[ea];W[bb]C[White lives.])
(;B[da];W[bb]C[White lives.]))
(;B[cb]C[];W[da]
(;B[ca];W[fa]C[This is ko. Black is able to kill unconditionally after wD19.])
(;B[fa];W[ac]
(;B[ea];W[ha]
(;B[ea];W[fa];B[ca]C[Ko, black could have killed unconditionally in this variation.RIGHT])
(;B[ca];W[fa]C[Ko, black could have killed unconditionally in this variation.RIGHT]))
(;B[ca];W[ba];B[ea];W[bb];B[ha];W[ab]C[Thanks to JottKa for this variation.RIGHT]))))
(;B[ea];W[cb])
(;B[da]
(;W[bb]
(;B[cb];W[ac]
(;B[ga];W[fa])
(;B[fa];W[ga])
(;B[ba];W[ab]
(;B[fa];W[ga])
(;B[ga];W[fa])))
(;B[ea];W[cb];B[ga];W[gb])
(;B[ga]
(;W[fa]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[gb];W[ha];B[ga];W[cb];B[gb];W[ac]C[You could have done better by playing E19 instead of G18 when G18 was first played.]))
(;W[cb];B[gb];W[ca]C[RIGHT]))
(;B[fa];W[cb]))
(;W[ga]
(;B[bb]
(;W[ba]
(;B[ac];W[ea])
(;B[ca];W[ea];B[aa]C[RIGHT]))
(;W[ac];B[ab];W[ea]
(;B[ba]C[RIGHT])
(;B[ca]C[RIGHT]))
(;W[ea];B[ba]))
(;B[ba]
(;W[ab];B[ac];W[bb];B[cb])
(;W[ac];B[ab];W[ea]
(;B[cb];W[ad]C[RIGHT])
(;B[bb]C[RIGHT])
(;B[ca]C[RIGHT])))
(;B[ab];W[ba]
(;B[bb];W[ca])
(;B[ca];W[ea];B[cb])))))
(;B[ga];W[fa]
(;B[gb];W[ha]
(;B[ga];W[gb];B[db];W[eb]
(;B[da]C[Correct. Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT];W[bb]
(;B[cb];W[ac]C[White lives. Black cannot approach.])
(;B[ea];W[ac];B[ga]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT]))
(;B[cb];W[ac]
(;B[ab];W[ba]
(;B[ca];W[ad]C[ko])
(;B[ad]C[ko])
(;B[da];W[bb]C[ko]))
(;B[ba];W[ab];B[da];W[bb])
(;B[da];W[bb])
(;B[ca]C[ko]))
(;B[ca];W[ac];B[bb];W[ab];B[ba]C[From here it can be either a ko or seki. Black can do better.]))
(;B[gb];W[ga];B[db];W[eb]
(;B[da]C[Correct.];W[bb]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[cb];W[ac]C[White lives.];B[ba];W[ab]))
(;B[ca];W[bb]
(;B[ea];W[da];B[cb];W[ac];B[ea]MA[da]C[Black can do better than ko.])
(;B[cb];W[ac];B[ea];W[da]MA[ea]C[Black can do better than ko.]))
(;B[cb];W[ac]
(;B[ab];W[ba];B[da];W[bb]C[Ko.])
(;B[ba];W[ab];B[da];W[bb])
(;B[da];W[bb];B[ba];W[ab])
(;B[ca]C[Ko.])))
(;B[db];W[eb]
(;B[da];W[bb]
(;B[cb];W[ac]C[White lives. Black cannot approach.])
(;B[ea];W[cb];B[gb];W[ca];B[ga]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[gb];W[cb];B[ga];W[ac]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT]))
(;B[gb];W[cb];B[ga];W[da]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[ga];W[gb];B[da];W[bb]
(;B[cb];W[ac]C[White lives. Black cannot approach.])
(;B[ea];W[ac];B[ga]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT]))))
(;B[db];W[eb]
(;B[da]C[RIGHT];W[bb];B[ea]C[RIGHT])
(;B[ca]C[At best, this leads to ko.]))
(;B[ha];W[gb];B[db];W[eb];B[da];W[bb]
(;B[cb];W[ac])
(;B[ac];W[cb]))
(;B[da];W[db];B[cb];W[eb];B[ca]C[RIGHT]))
(;B[da]
(;W[ga]
(;B[eb]C[RIGHT])
(;B[db];W[eb]
(;B[bb]
(;W[ba]
(;B[ac];W[ea])
(;B[ca];W[ea];B[aa]C[RIGHT]))
(;W[ac];B[ab];W[ea]
(;B[ba]C[RIGHT])
(;B[ca]C[RIGHT]))
(;W[ea];B[ba]))
(;B[ba]
(;W[ab];B[ac];W[bb];B[cb])
(;W[ac];B[ab];W[ea]
(;B[cb];W[ad]C[RIGHT])
(;B[bb]C[RIGHT])
(;B[ca]C[RIGHT])))
(;B[ab];W[ba]
(;B[bb];W[ca])
(;B[ca];W[ea];B[cb]))))
(;W[ea];B[db];W[eb];B[ga]
(;W[cb];B[gb];W[ca]C[Black can play H19 later.RIGHT])
(;W[gb]
(;B[fa]C[RIGHT])
(;B[ha]C[RIGHT])
(;B[bb]C[RIGHT])
(;B[cb]C[RIGHT])
(;B[ba]
(;W[cb];B[ca];W[ac];B[bb];W[ab]C[Black can ignore this move.RIGHT])
(;W[ab];B[bb];W[ac]C[Black can ignore this move.RIGHT])))))
(;B[eb];W[db]
(;B[ga];W[gb];B[cb];W[da])
(;B[da]
(;W[cb];B[fa];W[ea]C[Black can do better than ko.])
(;W[ea];B[cb];W[ca];B[ba];W[da];B[ab];W[ac]C[Ko, black takes first, black has a local threat of G19.]))))
(;B[db];W[eb]
(;B[bc];W[ae]
(;B[da];W[ga]
(;B[bb]
(;W[ba]
(;B[ac];W[ea])
(;B[ca];W[ea];B[aa]C[RIGHT]))
(;W[ac];B[ab];W[ea]
(;B[ba]C[RIGHT])
(;B[ca]C[RIGHT]))
(;W[ea];B[ba]))
(;B[ba]
(;W[ab];B[ac];W[bb];B[cb])
(;W[ac];B[ab];W[ea]
(;B[cb];W[ad]C[RIGHT])
(;B[bb]C[RIGHT])
(;B[ca]C[RIGHT])))
(;B[ab];W[ba]
(;B[bb];W[ca])
(;B[ca];W[ea];B[cb])))
(;B[ga];W[cb];B[gb];W[da]C[RIGHT]))
(;B[da];W[cb];B[bc];W[ca]
(;B[bb];W[ea];B[ad]C[RIGHT])
(;B[ad]C[RIGHT])
(;B[ga]
(;W[ea];B[ad]C[RIGHT])
(;W[ae];B[gb];W[ea]C[RIGHT])))
(;B[ga]
(;W[gb]
(;B[bc]
(;W[ae]
(;B[da]C[RIGHT];W[bb]
(;B[cb];W[ac]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[fa]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[ca];W[ba])
(;B[ba];W[ab]
(;B[ea]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[fa]C[Correct. In this sequence, white can make a ko for B19.])))
(;B[ab];W[cb];B[ac];W[ad])
(;B[ac];W[cb])
(;B[ea];W[cb])
(;B[fa];W[cb]))
(;B[cb]C[Another new variation, added thanks to JottKa and LCZLAPINSKI.RIGHT];W[da]
(;B[ca];W[fa]C[This is ko. Black is able to kill unconditionally after wD19.])
(;B[fa];W[ac]
(;B[ea];W[ha]
(;B[ea];W[fa];B[ca]C[Ko, black could have killed unconditionally in this variation.RIGHT])
(;B[ca];W[fa]C[Ko, black could have killed unconditionally in this variation.RIGHT]))
(;B[ca];W[ba];B[ea];W[bb];B[ha];W[ab]C[Thanks to JottKa for this variation.RIGHT]))))
(;W[cb]
(;B[bb];W[da];B[ad]C[RIGHT])
(;B[ad]C[RIGHT])))
(;B[cb]C[Thanks to LCZLAPINSKI for this variation.RIGHT]))
(;W[fa];B[bc]
(;W[ae];B[da];W[bb]
(;B[ea]C[RIGHT])
(;B[cb];W[ac])
(;B[gb];W[ha];B[ga];W[cb];B[gb];W[ac]C[Black could have done better in this sequence.RIGHT]))
(;W[cb]
(;B[ad]C[RIGHT])
(;B[bb];W[da];B[ad]C[RIGHT])))))
(;B[eb];W[db];B[ga];W[gb];B[bc];W[ae];B[cb];W[da]))
(;W[cb]
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[ga];W[gb]
(;B[eb];W[db]
(;B[ea];W[da]
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[fa];W[ha]
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT]))
(;B[ha];W[fa]
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])))
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT]))
(;B[bc]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT])
(;B[bd]C[Correct. With proper white play, the best that black should get is the C16 group.RIGHT]))
(;B[db];W[bc];B[eb];W[cc]
(;B[fa];W[ga]C[Ko.])
(;B[ga];W[fa]))
(;B[eb]
(;W[bc];B[ga];W[fa]
(;B[ea]C[RIGHT])
(;B[gb];W[ha]
(;B[ga];W[gb];B[ea]C[RIGHT])
(;B[gb];W[db];B[ga];W[ea]C[RIGHT])))
(;W[db]
(;B[bc]C[RIGHT])
(;B[bd]C[RIGHT])
(;B[ga];W[gb]
(;B[bc]C[RIGHT])
(;B[bd]C[RIGHT])
(;B[fa];W[ea]
(;B[bc]C[RIGHT])
(;B[bd]C[RIGHT])))))))
(;B[ga]
(;W[gb]
(;B[cc];W[db]
(;B[bd]C[Good. Black can get a bit more before playing B16 though.RIGHT])
(;B[cb]C[Correct. Thanks to LCZLAPINSKI for this variation.RIGHT];W[da]C[Correct. Thanks to LCZLAPINSKI for this variation.RIGHT]
(;B[bd]C[RIGHT])
(;B[ca];W[fa];B[bd]C[RIGHT])
(;B[ea];W[fa];B[ca];W[eb];B[bd]C[Correct, but a ko threat had been wasted with the E19 exchange.RIGHT])))
(;B[db];W[eb];B[cc];W[cb]
(;B[bc]C[Correct. All black should be able to get away with is the capture of the C16 stones.RIGHT])
(;B[bd]C[Correct. All black should be able to get away with is the capture of the C16 stones.RIGHT]))
(;B[eb];W[db];B[cc];W[bd];B[da]
(;W[cb];B[fa];W[ea]C[Ko, black can do better.])
(;W[ea];B[bc];W[ae];B[cb];W[ca];B[ba];W[ac];B[da]C[Ko, Black can do better.])))
(;W[fa]
(;B[gb];W[ha]
(;B[ga];W[gb];B[cc];W[bd]
(;B[bc];W[ae];B[db];W[eb];B[da]
(;W[bb]
(;B[ea]C[If white makes the mistake of saving her C16 group, black can get much more.RIGHT];W[ac];B[ga]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])
(;B[cb];W[ac]C[Black cannot approach.]))
(;W[cb];B[bb]C[RIGHT]))
(;B[db];W[eb];B[bc];W[ae];B[da]C[If white makes the mistake of saving her C16 group, black can get much more.RIGHT];W[bb]
(;B[cb];W[ac]C[White lives. Black cannot approach.])
(;B[ea];W[ac];B[ga]C[Starting at C17 might trick white into trying to save the C16 stones, allowing black to go for the larger group.RIGHT])))
(;B[gb];W[cc];B[ga]C[RIGHT];W[eb]C[If white makes the mistake of saving her C16 group, black can get much more.]))
(;B[cc]
(;W[bd]
(;B[bc];W[ae];B[db];W[eb];B[da];W[bb];B[ea]C[RIGHT])
(;B[db];W[eb];B[bc]
(;W[ae];B[da]C[RIGHT];W[bb];B[ea]C[RIGHT])
(;W[cb];B[bb];W[da];B[ad]C[Correct. Thanks to LCZLAPINSKI for this variation.RIGHT])))
(;W[cb]
(;B[bc]C[RIGHT])
(;B[bd]C[RIGHT])))))
(;B[cb];W[cc]C[White saves everything.])
(;B[db];W[cc]C[White saves everything.])
(;B[eb];W[db];B[ga];W[gb]
(;B[fa];W[ea])
(;B[cc];W[bd];B[bc];W[ae];B[cb];W[da])))