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Ongoing Game 1 Move 249
Difficulty: Beginner
Keywords: EndGame
In OngoingGame Black 249 is a response to White's one-point sente play. It is obviously large enough to require a response, but it still may be instructive to evaluate it. :-)
White 2 elsewhere. Black 3 - White 4 is sente. The five marked points are Black's territory.
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 White 1, yielding the same result as if Black played first. The only way Black could gain, on average, would be if White 2, taking the ko, did not threaten much. But it does. Now let's look at the follow-ups.
After Black 1 the two marked points are Black's territory.
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 one 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 one point, so they have a miai value of one point. Similarly, we reckon that Black has three points of potential territory at A, and that a play at A is worth two 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 White 3 is also ambiguous. None of that affects the value of B, or A.) 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. |