This corner is taken from a tournament game, played just some hours ago.
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[Weiß]PB[Schwarz]AW[da][db][dc][dd][fd][ae][ce][cf][bg][bh]AB[ca][cb][cc][bd][cd][de][df][cg][dg]C[White to play - can he kill the black corner?]PL[W]
(;W[bb]CR[bb]
(;B[ab]CR[ab]
;W[ba]CR[ba]C[Black is dead RIGHT CHOICE])
(;B[ad]CR[ad]
(;W[be]CR[be]
;B[ab]CR[ab]
;W[ba]CR[ba]C[Black is dead RIGHT CHOICE])
(;W[bf]CR[bf]
;B[ab]CR[ab]
(;W[bc]CR[bc]
;B[ba]CR[ba]C[Black lives])
(;W[ba]CR[ba]
;B[bc]CR[bc]C[Black lives]))))
(;W[ad]CR[ad]
;B[ac]CR[ac]
(;W[ab]CR[ab]
;B[bf]CR[bf]C[Black is alive])
(;W[be]CR[be]
;B[bb]CR[bb]C[Black lives]))
(;W[be]CR[be]
;B[ab]CR[ab]C[Black lives. For the continuation, please check the next two problems!])
(;W[ab]CR[ab]
;B[ad]CR[ad]
;W[be]CR[be]
;B[bb]CR[bb]
;W[ac]CR[ac]
;B[aa]CR[aa]C[This is only a ko]))