# Double Go / Discussion

Sub-page of DoubleGo
Better defence?

Herman: Correct me if I'm wrong, but isn't this a better defence for white? Now black's invasion has become pointless, and white gets 7 points, winning by 2. (Black must play at least one of the a marked points to prevent another point for white there)

You're right! Even more reason for B not to play this line. SiouxDenim

Example – part 2

W cannot defend both attacks, so uses half a move to defend the cut and half a move to make an attack on the bottom B stones.

Herman: Shouldn't white's second half move be at a? That way, white can live and will not lose any stones...

Example – part 2

W only has two eyes.

Better

Herman: Whoops, missed that :)
So how about this then? White will either make three eyes on the left, or get both moves a and get an eye there...

It's not easy this problem making malarky! I added the 3 White stones on the right to provide some threats, they weren't supposed to be an option for an eye :( I can't find an easy fix for the problem either. SiouxDenim

Boring example

This is about the simplest problem I can think of. B to kill some W stones.

Matti: Black cannot kill.

SiouxDenim: Let's play it out and see.

B goes for a split attack
W chooses to save the left group

White can choose to make 3 eyes for one group

B attacks the other group

W needs to make 3 eyes. Capturing only produces 2 eye spaces.

W captures, but only gets two eyes
B stops W from creating a third eye.
W removes legal plays for B

Now Black has a parity problem. The group on the right needs 3 stones playing within it, with a single stone played on the first move. Black has no sensible places to play the other half of the move. When I first analysed this, I assumed that Black could pass for half of a move. The rules as currently written don't make this clear.

B attacks the other group - option 2

Black can also attack the group on the right like this.

W plays for parity problems again

Alternatively, White can try to save both groups directly, by placing one stone on each side. Again, the aim is to get 3 eyes so a group can live.

W goes for a split defence
B chooses a group to kill

There are obviously only 2 eye spaces now on the left, so W makes the group on the right obviously alive and asks B to prove the group on the left is not seki

W clarifies the life of the group on the right

B has a parity problem again.

I can see good arguments either way for allowing and disallowing half-pass moves; it'll only matter in games with very little territory. I propose that a pass is for a whole move.

Less boring example

I think that the original problem is unambiguous if B has another liberty in the middle group.

Double Go / Discussion last edited by SiouxDenim on February 26, 2011 - 00:21
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