Maybe I'm blind and/or tired but I can't for the life of me see what white can do after black plays 2. Black can get two eyes and secure life at eihter a or b and I don't see a white move that would prevent him playing one of those. What am I missing?
$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | a b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | a b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Amelia,
You're right that white can't prevent black from playing either a or b, so killing is not an option. That doesn't mean that white can't be satisfied.
Re: Back on track
Posted: Tue May 14, 2013 1:27 pm
by Bill Spight
Boidhre wrote:So I came across a problem a few days ago and I thought it was interesting and some of the people on this thread may enjoy it. I'll hide the answers as solving the problem might be interesting for people:
$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | . . X O . . . . . $$ | . X X O . . . . . $$ | . . X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | 1 b X O . . . . . $$ | a X X O . . . . . $$ | . . X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
One leads to a ko or seki, Whites privilege, one leads to a seki. It doesn't take much reading to see which is which but it's interesting I think, I missed the ko on my first read through and thought there were two valid answers partially I think because I expected to find a seki there. I'm not posting full answers because of copyright etc but this is a pretty straightforward problem from here.
This is one of the oldest problems there is. Comments may be copyrighted, but certainly not the answer.
$$W Seki $$ ------------------ $$ | . 3 X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | . . X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W Bent Four $$ ------------------ $$ | 5 . X O . . . . . $$ | 1 2 X O . . . . . $$ | 3 X X O . . . . . $$ | . 4 X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
makes Bent Four in the Corner, which is dead by tsumego convention. (Even though it is sometimes seki under area rules.)
@Amelia
White cannot kill, but can White live?
Re: Back on track
Posted: Tue May 14, 2013 1:45 pm
by skydyr
Amelia wrote:Well...
Maybe I'm blind and/or tired but I can't for the life of me see what white can do after black plays 2. Black can get two eyes and secure life at eihter a or b and I don't see a white move that would prevent him playing one of those. What am I missing?
$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | a b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W White to Play $$ ------------------ $$ | . . X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | a b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
$$W White to Play $$ ------------------ $$ | C 3 X O . . . . . $$ | 1 a X O . . . . . $$ | 2 X X O . . . . . $$ | . b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W White to Play $$ ------------------ $$ | C 3 X O . . . . . $$ | 1 a X O . . . . . $$ | 2 X X O . . . . . $$ | . b X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
This sequence lets white capture 2 stones with B if black plays A, since it's a snapback if black tries to capture B.
$$W White to Play $$ ------------------ $$ | b . X O . . . . . $$ | 1 4 X O . . . . . $$ | 2 X X O . . . . . $$ | 3 a X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W White to Play $$ ------------------ $$ | . 5 X O . . . . . $$ | 1 . X O . . . . . $$ | 2 X X O . . . . . $$ | 3 4 X O . . . . . $$ | X X O . . . . . . $$ | O O O . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
This leads to seki.
I'm not sure that the capture is any different from seki, because white gains 4 points from the capture, but loses 4 points in the corner, but on the other hand, it's hard to call it seki in that case. I'm wondering now if I'm missing something or if the problem was misstated.
EDIT: the capturing solution is two points worse than seki, because black captured for 1 point and has 2 points of territory, while white has 2 prisoners and 2 points. In the seki, black has 1 point for the captured stone, and white has none.
Re: Back on track
Posted: Tue May 14, 2013 2:16 pm
by Amelia
Bill Spight wrote:@Amelia
White cannot kill, but can White live?
Huh. I found the seki now.
This is why I love go. I'll come back to this problem tomorrow.
Re: Back on track
Posted: Tue May 14, 2013 4:02 pm
by Boidhre
Amelia wrote:
Bill Spight wrote:@Amelia
White cannot kill, but can White live?
Huh. I found the seki now.
This is why I love go. I'll come back to this problem tomorrow.
Here's another one, it's a bit harder but it uses a different technique to make the seki that you may or may not have come across before:
$$B Black to Play $$ ------------------ $$ | . . . . . . . . . $$ | . . . O X . . . . $$ | . O O O X . . . . $$ | W O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | . 5 3 4 7 . . . . $$ | 1 2 6 O X . . . . $$ | . O O O X . . . . $$ | W O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
The other atari leads to a ko, 1 move approach for Black so doable if White is komaster. This is a seki as capturing leads to this shape after Black recaptures:
$$B Black to Play $$ ------------------ $$ | . X . O X . . . . $$ | X O O O X . . . . $$ | . O O O X . . . . $$ | W O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | . X . O X . . . . $$ | X O O O X . . . . $$ | . O O O X . . . . $$ | W O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
I may have made a mistake in the above, but it looks reasonable to me.
Edit:
There is also this unanswered problem shown, this also results in a seki. I haven't solved it yet but it might interest people.
$$B Black to Play $$ ------------------ $$ | . . . . 1 . . . . $$ | . 2 . O O X . . . $$ | . O O O X . X . . $$ | . O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | . . . . 1 . . . . $$ | . 2 . O O X . . . $$ | . O O O X . X . . $$ | . O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Again, is a mistake.
Re: Back on track
Posted: Tue May 14, 2013 4:44 pm
by mitsun
You are close to the right solution, but this shape is not seki.
$$W W is dead (bent four) $$ ------------------ $$ | . X . O X . . . . $$ | X O O O X . . . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$W W is dead (bent four) $$ ------------------ $$ | . X . O X . . . . $$ | X O O O X . . . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Re: Back on track
Posted: Tue May 14, 2013 5:21 pm
by Boidhre
That's twice now I've mistaken bent four in the corner for a regular seki. Good to find blind spots I suppose.
Another go:
$$B Black to Play $$ ------------------ $$ | . 2 6 4 . . . . . $$ | 1 3 5 O X . . . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | c 5 3 4 . . . . . $$ | 1 2 b O X . . . . $$ | a O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Ok, so I'm not sure if this is a seki or not given normal tsumego rules. White can force a ko here once they have the outside liberties with a but if white leaves it, it's a seki as a by Black returns the position to the above after capture and recapture and b by Black gives White an eye. Filling with c by Black removes the ko and leaves a seki.
Is this considered a seki under normal conditions? i.e. where the defender has the option of ko in the sequence but not the attacker?
Re: Back on track
Posted: Wed May 15, 2013 3:43 am
by amnal
Boidhre wrote:Filling with c by Black removes the ko and leaves a seki.
If black fills at c, white can just atari the shape and it's still ko.
$$B $$ ------------------ $$ | 1 X X O . . . . . $$ | X O 4 O X . . . . $$ | 2 O O O X . . . . $$ | O O X X X . . . . $$ | 3 X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B $$ ------------------ $$ | 1 X X O . . . . . $$ | X O 4 O X . . . . $$ | 2 O O O X . . . . $$ | O O X X X . . . . $$ | 3 X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
$$B Black to Play $$ ------------------ $$ | 2 1 . O . . . . . $$ | . O O O X . . . . $$ | O O O O X . . . . $$ | O O X X X . . . . $$ | X X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | 2 1 . O . . . . . $$ | . O O O X . . . . $$ | O O O O X . . . . $$ | O O X X X . . . . $$ | X X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Re: Back on track
Posted: Wed May 15, 2013 9:40 am
by Bill Spight
Boidhre wrote:Ah silly me. Thank you Bill.
Amelia, I apologise for cluttering your thread, I really should have done this somewhere else.
$$B Black to Play $$ ------------------ $$ | c 5 3 4 . . . . . $$ | 1 2 b O X . . . . $$ | a O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | c 5 3 4 . . . . . $$ | 1 2 b O X . . . . $$ | a O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Ok, so I'm not sure if this is a seki or not given normal tsumego rules. White can force a ko here once they have the outside liberties with a but if white leaves it, it's a seki as a by Black returns the position to the above after capture and recapture and b by Black gives White an eye. Filling with c by Black removes the ko and leaves a seki.
Is this considered a seki under normal conditions? i.e. where the defender has the option of ko in the sequence but not the attacker?
There is no tsumego convention for such positions, as far as I know. In a real game, the invader has an advantage in terms of making ko, because she has fewer stones at stake. So the usual result here is seki, because White will avoid making the ko, and Black cannot make a ko.
There is a flaw in this problem, from a practical point of view.
$$B Black to Play $$ ------------------ $$ | . 5 3 4 6 . . . . $$ | 1 2 . O X . a . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B Black to Play $$ ------------------ $$ | . 5 3 4 6 . . . . $$ | 1 2 . O X . a . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
There really should be a Black stone at or around "a", or can push out into Black territory and take away a number of points. (If it is not Black territory, White may connect or threaten to do so.)
$$B Black to Play $$ ------------------ $$ | . . 2 1 3 . . . . . $$ | . 4 . O X . . . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .
[go]$$B $$ ------------------ $$ | . 5 3 4 . . . . . $$ | 1 2 . O X . . . . $$ | . O O O X . . . . $$ | O O X X X . . . . $$ | . X . . . . . . . $$ | . . X . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]
Is this considered a seki under normal conditions?
You got it. This is considered seki. It would be a very rare game where W would want to start a ko, risking a 20 point loss in order to gain 6 points from two moves. And once B fills the outside liberties, even that possibility is gone.
Re: Back on track
Posted: Wed May 15, 2013 11:46 am
by Amelia
Boidhre wrote:Ah silly me. Thank you Bill.
Amelia, I apologise for cluttering your thread, I really should have done this somewhere else.
Please don't. I really like your interesting problems
I'm still baffled by the fact that in the first problem, white could make a seki despite black having two eyes. Two eyes in my book was a big sign "STOP READING HERE". It shouldn't be
And if I haven't posted anything about the second, that's because I haven't worked it out yet.
Re: Back on track
Posted: Wed May 15, 2013 1:00 pm
by Boidhre
Amelia wrote:Please don't. I really like your interesting problems
I'm still baffled by the fact that in the first problem, white could make a seki despite black having two eyes. Two eyes in my book was a big sign "STOP READING HERE". It shouldn't be
And if I haven't posted anything about the second, that's because I haven't worked it out yet.
Most of progression in go from ddk to sdk is learning about all the things we thought were true that really, really aren't. It probably applies when you're stronger too to a lesser extent, or on more minor issues.
The second problem is a bit cruel and nasty for you if until now two eyes = dead but reading things out when there's no time pressure can be fun. Really don't worry if you have trouble solving it, I didn't recognise the seki when I found it in my early readings of the problem.
Re: Back on track
Posted: Mon May 20, 2013 11:53 am
by Amelia
So I was at the Kido Cup the last three days. It was intense. I didn't fare very well in the tournament with only 2 wins in 7 rounds, though I did beat an 11 kyu. (On average the strength of my fellow DDKs seemed to have not so much to do with their actual ranking).
I met nice people (including Bonobo!) and got tons of games against stronger people between rounds, so basically it was go playing all day long. Yesterday evening, hoping to find an opponent but not daring to ask anyone, I just sat at a board, my whole body language screaming 'I wanna play'. After a couple of minutes, someone came to sit in front of me, and without a word, started playing. We had no idea who the other one was and how strong he was. It's going to be a while before I get to play a 1 kyu as white again ^^° He was nice to me. I only lost by 30 points. I also got a completely bewildering lecture about some joseki I had never heard about. In the end they had to kick me out at one in the morning while I was finishing one last game against a 4 kyu. The last round this afternoon was terrible, I was exhausted and defeated myself with a self-atari. I felt actually relieved that the game was over so I could just go and collapse on a bed somewhere.
Then I found out that the pro players were offering one on one fast games and anyone could participate, so I got myself two cups of coffee and asked for a game. Obviously I got wiped from the board, it was fascinating.
but 
refutes it:
makes Bent Four in the Corner, which is dead by tsumego convention. (Even though it is sometimes seki under area rules.)
is a mistake.
's end with a crush for two eyes for White.
can push out into Black territory and take away a number of points. (If it is not Black territory, White may connect or threaten to do so.)
