This strange corner position occured in a KGS game. There are some interesting variations besides the solution, so try navigate solution after solving it!
(;SZ[19]AW[ba]AW[db]AW[hb]AW[cc]AW[af]AW[df]AW[ag]AW[bg]AW[cg]AW[dg]AB[ca]AB[da]AB[fa]AB[eb]AB[ec]AB[dd]AB[fd]AB[ae]AB[ce]AB[bf]AB[cf]C[White to play]GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]RU[Japanese]KM[0.00]TM[]PW[Weiﾃηｸ]PB[Schwarz]PL[W]
(;W[bd];B[be]
(;W[ab]
(;B[ad];W[cb];B[ac];W[ea];B[bc]
(;W[da];B[bb];W[fb]C[White is out in the open - black A16 was too ambitious CHOICERIGHT])
(;W[bb];B[da]))
(;B[bb]
(;W[cb]C[Ko! This is best for both CHOICERIGHT])
(;W[bc]C[Ko! This is best for both CHOICERIGHT]))
(;B[bc]
(;W[ac];B[cd];W[ad];B[cb]C[CHOICE])
(;W[bb];B[cd];W[ac];B[ad]C[CHOICE])
(;W[cd];B[de]
(;W[bb]C[ CHOICERIGHT])
(;W[cb]C[ CHOICERIGHT])
(;W[ac]C[ CHOICERIGHT])))
(;B[cb]
(;W[bb];B[dc]
(;W[ad];B[bc]C[CHOICE])
(;W[ac];B[ad]C[CHOICE])
(;W[cd];B[ad]C[CHOICE]))
(;W[cd];B[de];W[bb]
(;B[dc];W[ad]C[White lives - this is worst for black CHOICERIGHT])
(;B[ad];W[ea];B[da]
(;W[ca];B[dc]C[In this variation (started with BC18) white can do better than a ko CHOICE])
(;W[ac]C[RIGHT])))))
(;W[cb];B[ab])
(;W[cd];B[de];W[ab]
(;B[ad];W[cb];B[ac];W[ea];B[bc]
(;W[bb];B[da]C[CHOICE])
(;W[da];B[bb];W[fb]C[White is out in the open. Black A16 was too ambitious CHOICERIGHT]))
(;B[cb];W[bb];B[dc];W[ad]C[White lives - this is worst for black CHOICERIGHT])
(;B[bb]
(;W[bc]C[Ko! This is best for both CHOICERIGHT])
(;W[cb]C[Ko! This is best for both CHOICERIGHT]))))
(;W[cb];B[bd]
(;W[bc];B[ab])
(;W[ea];B[bc]))
(;W[cd];B[de];W[bd];B[be];W[ab];B[bb]
(;W[bc]C[Ko This is best for both RIGHT])
(;W[cb]C[Ko This is best for both RIGHT])))