kb: All old content moved here
TODO: Amend the example. See my comment at the bottom of the page.
Adapted from Gokyo Shumyo, Section 1, Problem 21 / Solution.
White can live with either a or b, but plays kikashi with before living.
If White immediately takes a vital point, she lives too, but now she has failed to force Black. If White plays later in the game, the value of that move is reduced to 4+  points, and Black can choose to ignore it. If White eventually captures the stones with and , Black can make shape with and . Also, has now been turned into a superfluous move, a one-point loss.
The difference with the correct diagram is that, if Black ignores , then the capture of the stones yields not merely 4 points, but also life for the corner. Now look again at the previous diagram, which is as if White plays at a here, in exchange for a black move elsewhere, really a ridiculous turn of events. --DieterVerhofstadt
aLegendWai: I am not in a good position to raise argument because I am a very weak player. Anyway, I just try to express my hesitation. You may disagree with it entirely.
aLegendWai: As you said in the previous diagram, W can live by playing either "a" and "b". So I feel W is alive already.
TDerz: White would be dead after .
So the initial statement above could be rephrased "White plays kikashi before living with with either a or b."
kevinwm: Here's another way to think of it: w needs to move in order to live (eye space is a bulky-5). But instead, white can play a move that makes miai for life, by adding a new opportunity to make an eye. This is superior, because 1) b should respond now, rather than letting w live in sente, and 2) it threatens to make life with extra points. Given the choice between just living, or guaranteeing life by threatening to make another eye and extending - the latter is always better.
In this case, I don't feel the capture of 2 stones yields the gain of "life for the corner". W is already alive, so this gain is not a gain at all. Rather "the capture of 2 stones" saves 1 stone at "a".
What do you think?
Rich: What happens if black plays b first? The point is, W must play to live.
aLegendWai: Try to compare 2 cases.
W doesn't need to play at "a" and "b". W gains 2 more points.
W captured 2 . It gets 4 points (2 prisoner + 2 territories).
B has to play , . B loses 2 points.
There is an endgame move at "c,d,e". B has already lost 2 points at "c/d". And the endgame values 1-point. If W plays first, B will lose 1 more point.
By the way, B always gets sente in this endgame if both parties completes the endgame.
Thus the value of playing is 10(+1) points.
Any idea is welcome.
This is probably the last time I am going to say that.
aLegendWai: Here is what I feel about the gain of capturing 2 :
kb: This page could use a WME.
Bill: This page could use a complete rewrite. It is a go proverb, and all we have is an example or two, on of which sparked debate.
Is this really a proverb?