BQM 432

    Keywords: Question

HowToLose?: I generally practice by playing Go against myself. I was playing one of these games when the following position arose. I'm not much of a counter, so I didn't know the correct sequence.

Late yose  

I had just played the marked stone, making atari against the four black stones in late yose.

My question is, should black simply connect, or should he take the White stone? This is what I had:

Black defends  
End position  

Herman Hiddema: In this position, black gets 0 points, while white gets 4 (two prisoners and the two marked points)

Black captures (W2 at white+circle, B3 at B1, W4 at black+circle, B5 at white+circle)  

HowToLose?: Now, it seems as though the second diagram is better, but since I'm not any good at miai counting, I was wondering what the effect of the captured black stones in relation to white's territory, etc., would have on the final count. Thanks!

Herman Hiddema: There are some issues here on whether W4 at black+circle is the largest move at that moment for white, and the same question on whether B5 at white+circle is largest (black could play ko if he chooses). But lets ignore those issues and focus on the end positions given.

End position 2  

Herman Hiddema: In this diagram, black gets 3 points (one at the circle marked point, two prisoners taken at moves B1 and B3). White gets 4 points (one at the square marked point, three prisoners taken with W2).

Herman Hiddema: So overall, since both sequences are gote for black, the second one is three points better for black.

Tapir: You have to compare with white taking the black stones, so it is a 13 point gote / reverse sente (6 captured, 7 territory, 1 black defending vs. the one point score with black capturing first), which is not small.

fractic: You don't need to compare with white playing first if all you want to know which black move is better. And since 4 stones are in atari it's clearly not small.

Tapir: The number i wrote is meant to be deiri counting. Btw. the initial diagram description was 0 pt. and 1 pt. gote... that was the reason for my comment.

Large yose  

Bill: I have altered the diagram because the effect of a possible atari on the black+circle stone was not clear. Let's just say that the bottom left region is Black's territory.

White first  

Bill: W1 captures 4 stones for a local score of -13. (White scores are negative, by convention.)

Black first  

Bill: B1 saves the 4 stones and captures 1 White stone. The local count is -1, as we shall see. So the original position was a gote that gains 6 pts., and that is a medium large yose.

White sente  

B2 @ black+circle.

Bill: Later W1 is a 3 pt. sente for White.

White sente (2)  

Bill: Later W1 is a 1 pt. sente. At the end each player gets 1 pt. of territory, but White has captured 1 more stone than Black, so the local score is -1.

Bill: It should be obvious that simply connecting Black's four stones is worse than this. :) In fact, it is almost 2 pts. worse.

Difference game

Difference game (Black has one captive)  

Bill: As always, we can use a difference game to compare moves. We'll let Black take the White stone and White connect.

Black first  

B3 @ black+circle, W4 @ 2, B5 @ white+circle, W6 @ black+circle.

Bill: When Black plays first, B1 saves his three stones, then there is take and retake on the right. The end result is +4 for Black (counting the original captured stone, OC).

White first  

B2 @ black+circle

Bill: When White plays first, W1 takes 3 Black stones, and B2 takes back. Then W3 takes 1 stone.

White first (ii)  

W5 @ white+circle

Bill: Then B4 takes 3 White stones and W5 takes back.

White first (iii)  

Bill: Then B6 and W7 finish the play. Each player has captured 5 stones, but Black has 1 more pt. of territory. The result is Black +1.

Black wins the difference game no matter who plays first, so Black's play (taking the White stone) is better. :)

BQM 432 last edited by Dieter on October 21, 2008 - 18:03
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