XuanxuanQijingProblem251/Solution

See also: Under the stones problem 5

Table of diagrams
Placement
Forcing moves
Capture inside
Sacrifice
Seeming ko
Approach
Under the stones

...,.....,....
..O...........
.O.O..........
....O.O.......
XXXX..........
.O.XOOXX.X....
X..XXXO..,....
.XXXfgOOXX.X..
XOOOabcO..X...
.O..OdB1e......

OTF: Placement

Black starts with the placement B1. This is a difficult move to respond to. If white a or b, black will connect out with e. So white must prevent that. If white c, e or any point further to the right, black will play a and at least one of white's eyes will be false. So the only move that both prevents connecting out and prevents a false eye is d.

Note: f and g are miai, if white plays one in response to B1, black plays the other.

[Diagram]

Forcing moves

Now, black plays a series of forcing moves. B3 and B5 threaten to connect out, while B7 and B9 threaten to make the eye that would be formed by capturing B1 and B3 a false one. So each of black's responses is forced. After W10, black will go on to capture...

...,.....,....
..O...........
.O.O..........
....O.O.......
XXXX..........
.O.XOOXX.X....
X..XXXO..,....
.XXXOOOOXX.X..
XOOOXXaOO.X...
.O.B1..XXOX....

OTF: Capture inside

After the capture, white must play a immediately. Other moves will result in white's death due to double damezumari, because white doesn't have many liberties on either side.

[Diagram]

Sacrifice

In response to W12, black sacrifices two stones but can recapture one.

...,.....,....
..O...........
.O.O..........
....O.O.......
XXXX..........
.O.XOOXX.X....
X..XXXO..,....
.XXXOOOOXX.X..
XOOOXXOOO.X...
.O.XX.B1B2OX....

OTF: Seeming ko

After W16, the situation looks like ko. But black has yet another trick up his sleeve.

...,.....,....
..O...........
.O.O..........
....O.O.......
XXXX..........
.O.XOOXX.X....
X..XXXO..,....
B3XXXOOOOXX.X..
XOOOXXOOO.X...
B5OB6XXB4B1B2OX....

OTF: Approach

Black approaches with B17 and B19, allowing white to capture the black stones inside.

...,.....,....
..O...........
.O.O..........
....O.O.......
XXXX..........
.O.XOOXX.X....
X..XXXO..,....
XXXXOOOOXX.X..
XOOOB1.OOO.X...
XOO..O.OOX....

OTF: Under the stones

B21 finally finishes white off, capturing under the stones.


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