Spot the error

Bill Spight · Post by **Bill Spight** » Fri Aug 01, 2014 12:06 am

White should have won this game, but got jigo instead. Where did it all go wrong?

Enjoy!

RBerenguel · Post by **RBerenguel** » Fri Aug 01, 2014 12:41 am

bernanos · Post by **bernanos** » Fri Aug 01, 2014 3:10 am

RBerenguel · Post by **RBerenguel** » Fri Aug 01, 2014 3:14 am

Showed the problem to Antti on IRC

ez4u · Post by **ez4u** » Fri Aug 01, 2014 5:54 am

RBerenguel wrote:Showed the problem to Antti on IRC

...

Why? If he wants to to read L19 and reply, let him. But it seems he doesn't, so... Better that you use your contacts to bug him about updating his blog! :tmbup:

DrStraw · Post by **DrStraw** » Fri Aug 01, 2014 6:14 am

RBerenguel · Post by **RBerenguel** » Fri Aug 01, 2014 8:00 am

ez4u wrote:
RBerenguel wrote:Showed the problem to Antti on IRC

...

Why? If he wants to to read L19 and reply, let him. But it seems he doesn't, so... Better that you use your contacts to bug him about updating his blog!

We had been talking about endgame books and problems recently and he told me he likes them a lot, so I thought he may enjoy an easy problem for a change of what he may be currently doing

.

Re: blog, he is kind of following the "communicating vessels approach" (to phrase it like in Hushfield's trip post) for a while, since it was draining too much time (I think it was a suggestion by one of his teachers, but I'm not sure). But he likes writing, so I guess he either is close to writing something or getting closer to wanting to write no matter what

Cassandra · Post by **Cassandra** » Fri Aug 01, 2014 11:09 am

DrStraw wrote:
Seems like move 7 should be played on the left edge.

Bill Spight · Post by **Bill Spight** » Sat Aug 02, 2014 7:45 am

OK, now that you have gone to school on that one, here is an easy problem.

White to play and win.

Uberdude · Post by **Uberdude** » Sun Aug 03, 2014 4:14 am

RBerenguel wrote:
Re: blog, he is kind of following the "communicating vessels approach" (to phrase it like in Hushfield's trip post) for a while, since it was draining too much time (I think it was a suggestion by one of his teachers, but I'm not sure).

Btw, thought I'd just say before this phrase takes of it makes no sense to me as a native English speaker. Perhaps Knotwilg meant "competing interests"? (As in spending time on studying and improving at Go is a competing interest to blogging about it).

RBerenguel · Post by **RBerenguel** » Sun Aug 03, 2014 4:34 am

Oh, it made sense to me (OC, not a native English speaker.) Yes, they are kind of competing interests, I assume.

Bill Spight · Post by **Bill Spight** » Sun Aug 03, 2014 7:47 am

Solution.

Still no takers on the problem?

Dusk Eagle · Post by **Dusk Eagle** » Sun Aug 03, 2014 9:45 am

I calculated how much all the moves were worth but couldn't find the sequence to get tedomari and win the game. Nice problem.

Bill Spight · Post by **Bill Spight** » Sun Aug 03, 2014 10:03 am

Dusk Eagle wrote:I calculated how much all the moves were worth but couldn't find the sequence to get tedomari and win the game. Nice problem.

Well, it is a bit counter-intuitive.

lightvector · Post by **lightvector** » Sun Aug 03, 2014 8:31 pm

First problem:

After looking at Bill's posted solution:

Second problem:

Afterthoughts:

Some further thinking about it results in the following things that I think are true:
* Compared to "fair", getting tedomari at temperature T prior to a drop in temperature to T' gives (T-T')/2 extra points. Useful for calibrating a sense of how bad you should feel when your opponent steals a big move right out from under you.

* Meaning that compared to "opponent gets tedomari" at temperature T, getting tedomari prior to a drop in temperature to T' gives T-T' extra points.

* Going back over the variations in both puzzles, indeed in the jigo variations, black gets the last 1-point move *and* the last 0.75-point move, *and* the last 0.5-point move. Whereas in the white-winning variations, white gets the last one of all of these. Indeed, this sums to a difference of 1 point.

* So to rephrase, when all moves of temperature less than T are miai and your opponent gets the last move of temperature T, you get the maximally bad case. Because due to miainess, he also gets the last move of temperature T' for all T' < T. If instead of that you got one more final move of temperature T, you get all of them instead. Then, you can either do the accounting of the gain by adding T more points immediately because all the miai below cancels out, or you can do the accounting by adding (T-T') + (T'-T'') + (T''-T''') + ... + (T'^n - 0) points for winning every subsequent tedomari, which also sums up to T.

* Wait a minute. The game's score aside from komi has to be an integer...

* Okay, I think this means (absent any kos) you can completely ignore all moves whose values are less than 1 point for any possible endgame puzzle like this and focus only on who gets the last 1-point or greater move. This shortens the necessary reading a little bit.

Why is this? Well, the only case where you gain a whole point from getting the last 1-point move is when it also switches every smaller-than-1-point tedomari from against-you to favoring-you. Which is precisely when everything below is miai. Anything short of this fails to produce a whole point of improvement, meaning that it must produce 0 points of improvement since the difference in final outcomes must be an integer.

But of course, by the very fact that it's a puzzle, we know that it must matter. A puzzle where your choice can have no effect on the result would be boring. So it must be the case that the puzzle is set up so that everything below 1 point is miai.

Moreover, the integerness of the game's score also means that if you want to verify that it does matter who gets the last 1-point move (that is, you don't want to rely on the knowledge that the puzzle is a puzzle), all you have to do is play through *one* of the possible variations of moves with values less than 1 point and watch who gets the last move of each temperature. If both players share in the 1-point-or-smaller tedomari to any degree, then by integerness every other variation necessarily gives the same result and it doesn't matter. Otherwise it does matter.

Of course, ko could still mess this up.

Yay! Okay, time for bed.

Life In 19x19

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