Saturday, November 22, 2008

Tsumego of the Day



Black to play and live. (from Gokyo Shumyo)

8 comments:

Gwen said...

I would play S19 : it creates an eye at T19 and there is plenty of room for another eye around Q19...

Chris said...

s19 is the vital point for white to kill, so it seems kind of obvious that black can live by playing there. I can't find a way for white to kill after that - but I doubt its going to be that easy...

NannyOgg said...

Yes, s19 is one way to live. There is another move though which also lives. It hasn't been mentioned by anyone yet.

And of course, the question after that is: which of those two moves is better and why?

Enjoy!

Nanny

Steve said...

I'm an extreme beginner, but, I think the answer is Q19?

Anonymous said...

T17 also works and is better endgame.

ExplO

NannyOgg said...

Good find, explo, T17 works too.

But are you sure on the better endgame?

Nanny

Sec said...

@Steve: Q19 was my first thought, too. But it doesn't work. There is no eye on the left side (O19/P19), even if black plays P19. On the right side there is only one eye [W: T17, B: T18, W: S19]

AvatharTri said...

Nanny, T17 seems to definitely be better endgame. I'm not as strong as you, but here's my analysis:

Variation 1:
S19: White's M19 capture is sente (otherwise white Q19). Black must respond around p19/q19/q18, effectively giving black only 3-4 points in territory. Then white can tenuki, or move to the right side to stop black's sente T16. For the sake of analysis, let's say black gets the sente move in (as black probably eventually will either get that or an equally valuable gote instead). Black ends with 3-4 points of territory, and has pushed white's sealing in of the right side to line 15.

Variation 2:
T17: Now, white's M19 capturing move is gote (if white Q19, black R19, white P19, black Q18, white N19, black T19). Certainly if he ignores, than black's territory is 1-2 points smaller than with variation 1, but certainly his tenuki was worth more than 1-2 points, otherwise black wouldn't of tenuki-ed. So, black gets the sente move on bottom (as assumed with variation 1), which white can bring himself to seal off the side afterwards on line 13 or 14. A similar shut in as with black S19 is possible after black T16 with white Q16, black Q18, white P19, black T19, white T14, and etc, leading to a situation where black is 0-2 points smaller, and white is 0-2 smaller than in S19's variation, but that's after black got in a free tenuki.

So it seems that the only way for T17 to be inferior is if white's T16 was sente, and it's not I believe. Certainly if black ignores it then the situation after white T19, black S19, is the same as in variation 1 (so white now captures in sente etc.) except white got in T16 for T17 for free, but black got a tenuki off. This would be the same as in variation 1 with white playing his sente capture, then playing T16 as reverse sente (slightly inferior), except that black got the 1 pt gote move of T17 for free (in addition to a tenuki and a free capture).

So the T17 response seems to me to be universally better, why do you think S19 may be better?