(;GM[1]FF[3]
RU[Japanese]SZ[9]HA[0]KM[0.5]
PW[]
PB[]
GN[ (W) vs. (B)]
DT[2002-04-28]
SY[Cgoban 1.9.5]TM[-];PL[1]
C[Black has played at A and white answered servile at B. There is a 0.5 komi
and no captures were made. How does black win now? ] LB[ag:A]
AW[fb][hb][fc][ed][de][fe][ge][he][ie][cf][ef][bg][cg][dg][eg][fg][ig][ah][dh][di]
AB[cb][eb][bc][ec][cd][dd][be][ce][bf][ff][gf][hf][if][ag][gg][eh][fh][gh][ei]
LB[ah:B]
(;B[af]PL[2]C[
];W[hh]
C[This move is worth 7 points in gote. B2 is only 5 points in gote. So white didn´t answer a4.
]
(;B[hi];W[gi];B[fi];W[ih]
C[White gets a gote seki and wins the game by half a point.
This seki is worth 7 points in gote.
])
(;B[hg]
(;W[hi];B[ih];W[gi]
C[White gets a gote seki and wins the game by half a point.
White made 7 points in gote here
])
(;W[gi];B[ih];W[hi]
C[White gets a gote seki and wins the game by half a point.
White made 7 points in gote here
])
)
(;B[ih];W[hi];B[hg];W[gi]
C[White gets a gote seki and wins the game by half a point.
White made 7 points in gote here
])
(;B[gi];W[hi];B[ih];W[ii]
C[White gets a gote seki here. B G1 wasted another two points compared with B H1 for example. White wins by 2.5 now.
])
)
(;B[fa];W[ga]
C[White should´t play here (compare the B a4, W h2 path), but even this proves the black move wrong: Black E9 and he has gotten only 2 points in gote. The lower left is bigger.
And if Black tenuki (plays elsewhere) he has gained nothing on the upper side (actually he lost something there).
])
(;B[gi];W[af]C[G1 leaves bad aji in that corner.
]
(;B[fa];W[ga];B[ea];W[ae];B[ad];W[ag]C[White wins by half a point
])
(;B[ae];W[ea]C[White cannot avoid the ko at a3 or he looses.
];B[da];
W[fa];B[ag];W[db];B[dc];W[af]
C[Now it dawns to black that he had been too carelessly about the lower right (W h2 is a ko threat)
]
;B[fd];W[gd];B[ag];W[hh]
(;B[bh];W[hi];B[ih];W[ii]
C[Seki. Blacks gain in the other corner doesn´t make up for it.
])
(;B[af];W[hi];B[ih];W[ii]
C[Seki. Blacks gain in the lower left does´t make up for it.
])
)
)
(;B[hi];W[af]C[H1 leaves bad aji in that corner.
]
(;B[fa];W[ga];B[ea];W[ae];B[ad];W[ag]C[White wins by half a point
])
(;B[ae];W[ea]C[White cannot avoid the ko at a3 or he looses.
];B[da];
W[fa];B[ag];W[db];B[dc];W[af]
C[Now it dawns to black that he had been too carelessly about the lower right (W h2 is a ko threat)
]
;B[fd];W[gd];B[ag];W[hh]
(;B[bh];W[gi];B[fi];W[ih]
C[Seki. Blacks gain in the other corner doesn´t make up for that.
])
(;B[af];W[gi];B[fi];W[ih]
C[Seki. Blacks gain in the other corer doesn´t make up for it.
])
)
)
(;B[hg];W[af]C[H3 leaves bad aji in that corner.
]
(;B[fa];W[ga];B[ea];W[ae];B[ad];W[ag]
C[Sorry, but Black could not avoid the ko at a4. White wins by half a point
])
(;B[ae];W[ea]C[White cannot avoid the ko at a3 or he looses.
];B[da];
W[fa];B[ag]C[
];W[db];B[dc];W[af]
C[Now it dawns to black that he has been too carelessly about the lower right corner
(White H2 is a ko threat)
]
;B[fd];W[gd];B[ag];W[hh]
(;B[af];W[hi];B[ih];W[gi]C[Seki
])
(;B[bh];W[hi];B[ih];W[gi]C[Seki
])
)
)
(;B[ih];W[af]C[J2 leaves bad aji in that corner.
]
(;B[fa];W[ga];B[ea];W[ae];B[ad];W[ag]C[White wins by half a point
])
(;B[ae];W[ea]C[White cannot avoid the ko at a3 or he looses.
];B[da];
W[fa];B[ag];W[db];B[dc];W[af]
C[Now it dawns to black that he had been too carelessly about the lower right (W h2 is a ko threat)
]
;B[fd];W[gd];B[ag];W[hh]
(;B[bh];W[hi]
(;B[hg];W[gi]C[Seki
])
(;B[gi];W[ii]C[Seki
])
)
(;B[af];W[hi]
(;B[hg];W[gi]C[Seki
])
(;B[gi];W[ii]C[Seki
])
)
)
)
(;B[hh];W[af]
C[Black has catched himself just in time and changed his play to the correct
place (H2). Both players should have played there instead of A and B at the
problem start. You got it right. Just proceed for 2 or 3 moves. ]
(;B[ae];W[ea];B[da];W[fa];B[ag]
C[RIGHT
None of the players could avoid the ko at a3.
Now you see why H2 is the only correct move in the lower right. This way white
has only one ko threat at d8 (the c9 threat later is too small). So black wins this
ko (he has a threat himself at f6) and thus the game.
])
(;B[fa];W[ga];B[ea];W[ae];B[ad];W[ag]
C[Sorry, but black could not avoid the ko at a3. White wins by half a point.
])
)
)