If it's black to move, where should he play?

I was in a similar position when white played on H2, and I played on G1. White kept playing in there for a little bit but eventually stopped. I decided to ignore all that activity. At the end of the game, my group was deemed dead. Why, if I had two eyes?

I can't believe I still don't understand this game!

micronesia

United States24753 Posts

November 10 2012 05:19 GMT

If you play at G1 you don't have two eyes, yet. White could play H1,G2, and finally F1 to capture the G1 stone. It's only two eyes if none of the stones in the group can be captured by consecutive moves by the opponent.

edit: I'm rusty on my go but I think the idea is for YOU to play H2 before the opponent does, in that situation. Whichever way white responds you can finish creating the two eyes.

Hesmyrr

Canada5776 Posts

November 10 2012 05:44 GMT

http://senseis.xmp.net/?FalseEye
Needs to play at G2 to make stone at G1 work.

AmericanUmlaut

Germany2591 Posts

November 10 2012 11:02 GMT

If it's black to play, you can play at G1, J3 or H2, those all make the group unkillable. Technically, you can even play at G2 or H3 to make the group unkillable. If black plays elsewhere or passes, and white plays at H2, then the black group is dead. From that position, the only two potential eyes you can make are at F1 and J4, but both of those eyes would require two uninterrupted moves to make, so you'll be blocked and killed from that position regardless of what you do.

Edit: Oh, and to answer your question about why the group was actually dead, the link to Sensei's Library in the post above me is the correct answer. The one stone at G1, since it's not connected to the large group of stones, is still killable, so the "eye" that it makes is a false eye.

BrTarolg

United Kingdom3574 Posts

November 10 2012 11:04 GMT

On November 10 2012 20:02 AmericanUmlaut wrote:
If it's black to play, you can play at G1, J3 or H2, those all make the group unkillable. Technically, you can even play at G2 or H3 to make the group unkillable. If black plays elsewhere or passes, and white plays at H2, then the black group is dead. From that position, the only two potential eyes you can make are at F1 and J4, but both of those eyes would require two uninterrupted moves to make, so you'll be blocked and killed from that position regardless of what you do.

Edit: Oh, and to answer your question about why the group was actually dead, the link to Sensei's Library in the post above me is the correct answer. The one stone at G1, since it's not connected to the large group of stones, is still killable, so the "eye" that it makes is a false eye.

If white gets h2 i think you can still ko by playing on the 2-1 points

AmericanUmlaut

Germany2591 Posts

November 10 2012 11:10 GMT

On November 10 2012 20:04 BrTarolg wrote:

Show nested quote +

If white gets h2 i think you can still ko by playing on the 2-1 points

Maybe I'm misunderstanding what you mean, but I'm pretty sure that's not right:

W: H2
B: H1
W: J2

That blocks a ko. Black needs to be able to play at both H1 and J2 to set up a ko, but there's no reason that white has to allow that to happen.

incnone

17 Posts

November 10 2012 12:40 GMT

Consensus here seems to be that if white plays H2 then black's group is dead. I disagree: black can respond to H2 with

W: H2
B: G1
W: G2 (otherwise B plays G2 for life)
B: J3
W: H3 (otherwise B plays H3 for life)
B: H1

and white is now short on liberties on the inside group. So it seems to me that black should tenuki.

Edit: I take the above back, since (as vflux comments below) white actually makes seki after (W)H2 (B)G1 (W) J3, since now:

(B) G2 ends in a seki after (W) H1 (making miai of H3 and J2);
(B) H3 ends in a seki after (W) J2; and
(B) H1 ends in a seki after (W) G2.
(B) J2 ends in a seki after (W) G2.

Tal

United Kingdom1017 Posts

November 10 2012 13:39 GMT

Yeah H2 leaves you perfectly safe. Whereas if white plays there, you won't be able to make two true eyes.

vflux

New Zealand118 Posts

November 10 2012 14:07 GMT

The black group is alive as is, you can just tenuki.

Although I think w can get a gote seki with H2 G1 J3.

MasterOfChaos

Germany2896 Posts

November 10 2012 15:17 GMT

#10

Looks like seki if w moves first, and two eye alive if b moves first.

As black I'd tenuki and try to live in the top left. It will probably fail, but if you don't the game is already lost.