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Ongoing Game 1 Move 249
  Difficulty: Beginner   Keywords: EndGame

In OngoingGame B 249 is a response to White's 1 point sente. It is obviously large enough to require a response, but it still may be instructive to evaluate it. :-)

[Diagram]
Diag.: B 249: Black plays first.

W 2 elsewhere.

B 3 - W 4 is sente. The 5 marked points are Black territory.


[Diagram]
Diag.: B 249: White plays first.

Black can reply at a, making ko. The ko is complicated, but does not seem to gain anything on average, by comparison with simply filling. The worst that Black threatens is to take W 1, yielding the same result as if Black played first. The only way Black could gain, on average, would be if W 2, taking the ko, did not threaten much. But it does.
If Black does make the ko with B a, for White to connect at W 3 is usually inferior. Normally it is better to play elsewhere instead.

Now let's look at the follow-ups.


[Diagram]
Diag.: Black follow-up.

After B 1 the 2 marked points are Black territory.


[Diagram]
Diag.: White follow-up.

White takes away the rest of the points at stake.



Now we can make a game tree:

                         A
                        / \
                       /   \
                      5     B
                           / \
                          2   0

A stands for the original position, B stands for the position after White plays.

We reckon that Black has 1 point of potential territory at B, the average of the result of Black's gote and White's gote. Each gote play from B gains 1 point, so they have a miai value of 1 point.

Similarly, we reckon that Black has 3 points of potential territory at A, and that a play at A is worth 2 points.

(Note: B is actually ambiguous. Instead of taking gote White can simply play at 3 with sente. Well, sort of sente. The position after W 3 is also ambiguous. None of that affects the value of B or A.)

--BillSpight



This is a copy of the living page "Ongoing Game 1 Move 249" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.