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Offline RobertJasiek
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #21 Posted: Wed Jan 01, 2020 3:09 am 
Judan

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It is often complex to verify whether a monkey jump is sente, ambiguous or gote, and so to verify whether calculated move values and counts are correct. In these examples, assumptions about the left outside need to be made.
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Offline jlt
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #22 Posted: Wed Jan 01, 2020 12:00 pm 
Gosei
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Probably for the problem to make sense, we need to assume that both moves a and b are sente. However I don't see the difference between problems 50 and 51 so I must be misunderstanding something.
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Offline xela
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #23 Posted: Wed Jan 01, 2020 3:24 pm 
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jlt wrote:
Probably for the problem to make sense, we need to assume that both moves a and b are sente. However I don't see the difference between problems 50 and 51 so I must be misunderstanding something.


The difference is the presence or absence of a white stone at P17. I was surprised to find that makes a difference to some of the follow-up moves, which is why I find it an interesting pair of problems.

No, you don't assume something is sente, you figure out which continuation makes it into a sente sequence!

RobertJasiek wrote:
It is often complex to verify whether a monkey jump is sente, ambiguous or gote, and so to verify whether calculated move values and counts are correct. In these examples, assumptions about the left outside need to be made.


Thanks Robert, this hadn't occurred to me. Now I'm thinking of things like this:

Click Here To Show Diagram Code
[go]$$Bc What's on the left?
$$---------------------+
$$ . . . . 3 1 4 . . . |
$$ . a . . . 2 . . X . |
$$ . . O . O . O O X . |
$$ . . . . . O . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . X . . . |
$$ . . . . . . . . . . |[/go]

If there are black stones near a, then perhaps white shouldn't play this :w2:. Even if there are black stones further away to the left, the potential for black to play around a may affect the local endgame moves. For this problem, we'll assume that black doesn't have any stones that are near enough and strong enough to cause trouble, so that in this diagram, :b1: and :b3: are captured with no bad aji left behind.

Is that the sort of thing you had in mind?
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Offline RobertJasiek
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #24 Posted: Wed Jan 01, 2020 11:11 pm 
Judan

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It is very much more demanding than that. For each interesting first move, study whether it in its alternating sequence is sente, ambiguous or gote and how long it is worth playing successively. Then compare different first moves to determine which should usually be played in the local endgame. Each of these aspects must be assessed by value conditions.

To assess values, we must make assumptions on the left side (Is there white territory? Where does White's territory end? Can Black escape?) and the life of the white group (Which attacking moves must be answered because sacrifice of a tail is considered too expensive?). The problems would be somewhat simpler if at least assumptions would not have to be made in simplified positions, such as:

Click Here To Show Diagram Code
[go]$$B
$$-------------------------+
$$ O . X X X . . . . . . . |
$$ O . X X X . . . . . X X |
$$ O O O O X . O . O O X . |
$$ O . O . O O O O O X X X |
$$ O O O O O . . . . X X . |
$$ X X X X X X X X X X X X |
$$ . . . . . . . . . . . . |[/go]
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Offline jlt
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #25 Posted: Thu Jan 02, 2020 1:55 am 
Gosei
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There may exist whole board situations where a and b are not sente, for instance if there is a sufficiently big point elsewhere on the board, White doesn't need to respond to :b1: or :b3:. That's why I think we should assume that :b1: is sente for the problem to make sense.

Click Here To Show Diagram Code
[go]$$Bc
$$+------------------------------+
$$|. O O . . . . . . . . . 3 . 1 . . . . |
$$|O . O . . . . . . . . . . . . . . X . |
$$|O O O O O O O O O . O . O O O O O X . |
$$|. . . . . . . . . . . . . X X . X . . |
$$|. . . . . . . . . . . . . . . . . X . |
$$|. . . . . . . . . . . . . . . . X . . |
$$|. . . . . . . . . . . . . . . . . . . |[/go]


Now, even with this assumption, I am missing something.

Let's have a look at problem 51.

Click Here To Show Diagram Code
[go]$$Bc Black plays a with sente
$$---------------------+
$$ . . . . 4 1 . 3 . . |
$$ . . . . . 2 . . X . |
$$ . O . O O O O O X . |
$$ . . . . X X . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |[/go]




White finishes later the sequence, W+1.5? (points are counted in the rectangle O19-S18)

Click Here To Show Diagram Code
[go]$$Bc White finishes later the sequence,
$$---------------------+
$$ . . . . 4 . 6 3 . . |
$$ . . . . . 2 . 7 X . |
$$ . O . O O O O O X . |
$$ . . . . X X . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |[/go]



If Black plays b with sente:

Click Here To Show Diagram Code
[go]$$Bc Black plays b with sente, W+3
$$---------------------+
$$ . . . . . 2 1 3 7 . |
$$ . . . . . . 4 6 X . |
$$ . O . O O O O O X . |
$$ . . . . X X . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |[/go]


So a seems to be better than b by 1.5 points ?

And I don't see why the sequences should be different in problem 50.
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Offline xela
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #26 Posted: Thu Jan 02, 2020 3:41 am 
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jlt wrote:
There may exist whole board situations where a and b are not sente, for instance if there is a sufficiently big point elsewhere on the board, White doesn't need to respond to :b1: or :b3:. That's why I think we should assume that :b1: is sente for the problem to make sense.

OK, I see the point. Yes, we assume that black won't play :b1: until such time as :b1: is actually a good move. Most of the time that means it will be sente. The book Endgame 2 - Values discusses this sort of thing in more detail using the terms "local sente" and "global sente".

jlt wrote:
Now, even with this assumption, I am missing something.

I agree with your analysis of the second position. (Again, no guarantee that my counting is correct, but at least it's reassuring that we both get the same answer!) Where the first one differs is:
Click Here To Show Diagram Code
[go]$$Bc Problem 49, response to small monkey jump
$$---------------------+
$$ . . . . . 2 1 a . . |
$$ . . . . . c . 3 X . |
$$ . . O . O b O O X . |
$$ . . . . . O . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . X . . . |
$$ . . . . . . . . . . |[/go]

Now black can play :b3: instead of a and still keep sente. With no white stone at b, white will have to come back and defend the cutting point at c.

The book gives this move order (next diagram), which I think amounts to the same thing:

Click Here To Show Diagram Code
[go]$$Bc Problem 49, correct answer according to Shirae
$$---------------------+
$$ . . . . . a 1 d . . |
$$ . . . . . 2 c b X . |
$$ . . O . O . O O X . |
$$ . . . . . O . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . X . . . |
$$ . . . . . . . . . . |[/go]


I'm assuming that white a through black d would follow at a later stage. For the large monkey jump, the book gives the same variation in both problems (although with :w2: and :w4: in the opposite order; I'm not sure if there's a reason for that, or if it's just a way of showing us that both move orders are possible). So in this position, the small monkey jump is half a point better for black than the large monkey jump.

Compared with problem 50:
Click Here To Show Diagram Code
[go]$$Bc Black plays b with sente, W+3
$$---------------------+
$$ . . . . . 2 1 3 7 . |
$$ . . . . . a 4 6 X . |
$$ . O . O O W O O X . |
$$ . . . . X X . X . . |
$$ . . . . . . . . X . |
$$ . . . . . . . X . . |
$$ . . . . . . . . . . |[/go]

in problem 49, white has lost the point at a, and black has an extra point at :b7:. So when the :wc: stone is missing, the small monkey jump gains an extra two points.


For what it's worth, the book's assessment of relative values is
Problem 49: the large monkey jump "takes a slight loss".
Problem 50: in response to the small monkey jump, " :w2: is too good".

I don't know why he doesn't use numbers. It looks like "a slight loss" is exactly half a point, and "too good" is exactly 1.5 points, unless there's another complication that I'm missing.

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Offline Uberdude
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #27 Posted: Thu Jan 02, 2020 4:02 am 
Judan

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Here is a real-game endgame problem with relevance to the current discussion from a recent game of mine (white).

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . a . . . . . . |
$$ | . X O O . O . . . . O O . X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O 1 O . X . X O X . . |
$$ | . X X O O O O . . X . . . X O . O . . |
$$ | . O X O . O X O . . . . X O O O O . . |
$$ | . 2 O O O X X X X , . . . X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


n18 is a classic "double sente" endgame kosumi on the 2nd line, but I decided it was not sente enough for me to play now as I feared a black tenuki to close the lower side at l6. If I followed up with a monkey jump, I thought another black tenuki was plausible kiai as to answer would only preserve another half-dozen or so points in gote and black's group was already super strong. So I decided that it was better for me to poke into the lower side in what I thought was sente for some benefit there and then play n18. I wasn't sure what the best spot was, but went for L5. My opponent resisted my plan and took n18 for himself, but then I broke into the lower side which was pretty big too but gote, so he got the monkey jump in sente on the top. I didn't make any precise value calculations, I wonder what they would indicate as best play. n10 is also a very big move for white with reverse sente characteristics as black moves there have some attacking potential on the white group so maybe white taking n18, allowing black l6 and then n10 is ok to get tedomari (but is s3 much smaller?).

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Offline xela
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #28 Posted: Thu Jan 02, 2020 4:27 am 
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Thanks Uberdude, that's a really interesting example, and points to a problem that I have when trying to apply endgame theory.

I'm confident that, given enough time and willpower, I could count the value of a move at N18. But counting the move value for L5 is much harder for me, not because of the counting itself, but because I'd have a hard time actually trying to decide whether L5 is indeed the best local move for white, or whether I want to start at M6 or M5 instead, or whether the cute-looking K5 is playable, let alone black's correct responses to each of those moves, whether the sequence finishes in sente or gote, and the right move if black gets to go first in that area...

So counting works OK (if I've got enough time left on the clock) once all the groups are settled and there are no "vague-looking" areas, but in a position like your diagram I'm much more in "middlegame mode" rather than "endgame mode", even though I know the endgame is supposed to start a bit earlier.

(Trying to do the calculations in my head -- and falling back on traditional endgame theory, because there's no such thing as sente in modern endgame theory -- I get a swing value of 6 points for N18. Slightly smaller than I would have guessed because N17 turns into a sente follow-up for whoever goes second, which cancels out some of the gain. I look forward to being told where I went wrong.)
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Offline Knotwilg
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #29 Posted: Thu Jan 02, 2020 4:59 am 
Oza
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In Uberdude's game I count White ahead by a couple of points (I don't know how many prisoners there are). In such a situation I will go for A, the "double sente" at the top, because it has a higher degree of certainty, i.e. it's harder to see how Black can get more points from developing the bottom while allowing White to monkey. If I had counted White behind, I would go for L5, which is the harder value to calculate and brings uncertainty into the game.

Also, after A, White doesn't need to follow-up with a monkey, but can choose to play the next big gote N10 or S3. Here I would probably go for S3 again because I find it easier to gauge its size and be confident it is big enough.

Uberdude's decision to L5 instead, indeed shows fighting spirit, or the lucidity to reflect on Black's kiai but in fact it entices Black to show such kiai and take A for himself, taking the opportunity for turmoil.

These musings have nothing to do with precise value computations, everything with maximizing the chance of winning and/or minimizing the effort to compute the result.

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Offline Uberdude
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #30 Posted: Thu Jan 02, 2020 5:13 am 
Judan

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Knotwilg wrote:
In Uberdude's game I count White ahead by a couple of points (I don't know how many prisoners there are). In such a situation I will go for A, the "double sente" at the top, because it has a higher degree of certainty, i.e. it's harder to see how Black can get more points from developing the bottom while allowing White to monkey. If I had counted White behind, I would go for L5, which is the harder value to calculate and brings uncertainty into the game.


Black has 5 captures to white's 1, and it's 6.5 komi. I thought I was a little ahead, but not enough to be slack.
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Offline Kirby
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #31 Posted: Thu Jan 02, 2020 5:29 am 
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n18 seems bigger to me than L5...

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Offline Uberdude
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #32 Posted: Thu Jan 02, 2020 7:24 am 
Judan

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Let's try to quantify how big l5 is then. Locally the game went as follows,

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . 2 . . . . . . |
$$ | . X O O . O . . . . O O . X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . 7 . 9 8 . X O . O . . |
$$ | . O X O . O X O 6 5 1 . X O O O O . . |
$$ | . X O O O X X X X , . 3 4 X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


And then after black had got s3 (so lower right super alive) he played to increase territory on left and damage right in sente, which did actually surprise me as I thought m2/m3 was likely best local yose for him, but lets count this instead of the ambiguous position above. So here white spent 2 moves to get 2 points at k6 and reduced black to the triangled territory.

Click Here To Show Diagram Code
[go]$$Bcm10
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . X . . . . . . |
$$ | . X O O . O . . . . O O . X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . O . O X . X O . O . . |
$$ | . O X O . O X O X O O . X O O O O . . |
$$ | . X O O O X X X X , . O X X X O . . . |
$$ | X . X X O O X . T . 1 2 6 . . X O B . |
$$ | . X . . X X . X T T 5 3 4 . X T X . . |
$$ | . . . . . . . . T T T . . . . X . . . |
$$ ---------------------------------------[/go]


Compared to black first at l6: the same triangles are marked and squares are the extra black territory. There's 20 of them. So that's swing of 22 for 3 moves difference or 7 1/3 points per move. (I ignore slight change at h5 because when black defends white gains by saving that in sente, but black gains by getting h8 peep to help with centre thinness.)

Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . a . . . . . . |
$$ | . X O O . O . . . . O O . X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O 2 X . X O X . . |
$$ | . X X O O O O . . X 1 3 . X O . O . . |
$$ | . O X O . O X O 4 5 S S X O O O O . . |
$$ | . X O O O X X X X S S S S X X O . . . |
$$ | X . X X O O X . T S S S S S S X O . . |
$$ | . X . . X X . X T T S S S S X T X . . |
$$ | . . . . . . . . T T T S S S S X . . . |
$$ ---------------------------------------[/go]


Now for the top, if black spends 1 gote and gets sente monkey jump:

Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . 6 3 5 9 . . . . . . . |
$$ | . . . . . . . . 0 4 8 7 1 B . . . . . |
$$ | . X O O . O . . . . O O W X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . . X . . . X O . O . . |
$$ | . O X O . O X O . . . . X O O O O . . |
$$ | . X O O O X X X X , . . . X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


If white spends 2 gotes then I don't know how to count top right for black, but white has gained 8 squares compared to before.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . S S S S S . . 3 . . . |
$$ | . . . . . . . . S S S . 1 . . . . . . |
$$ | . X O O . O . . . . O O . X . X . . . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . . X . . . X O . O . . |
$$ | . O X O . O X O . . . . X O O O O . . |
$$ | . X O O O X X X X , . . . X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


If black gote, he has 8 points (squares) in corner beyond triangles.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . 5 7 3 4 S S |
$$ | . . . . . . . . . . . . 1 . . 6 8 S S |
$$ | . X O O . O . . . . O O . X . X S S S |
$$ | . . X O . . . . O O X X X . X , X X S |
$$ | . . O . . . . . O X X . . X . X O T T |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . . X . . . X O . O . . |
$$ | . O X O . O X O . . . . X O O O O . . |
$$ | . X O O O X X X X , . . . X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


If white gote, then white is creating followup at a which actually makes ~4 points in the corner, and black's move there only makes ~3, so let's say current value is 2 for white, 1.5 for black so net -0.5 for black which I will round to 0. So if black gote was 8 and white gote was 0 then current value is black expects 4 points.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . 3 . . . |
$$ | . . . . . . . . . . . . 1 . . . 5 . . |
$$ | . X O O . O . . . . O O . X . X . a . |
$$ | . . X O . . . . O O X X X . X , X X . |
$$ | . . O . . . . . O X X . . X . X O . . |
$$ | . . . . . . . . . . . O O . O X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . X . . . . O . O O . O . . . O X X . |
$$ | . O O O O . . . . X . . . . . O X O . |
$$ | . O X X X X . X . , . . . . . O O X . |
$$ | . O O X . . . . . X . X . . . O X . X |
$$ | . X X X O O . . . . . . . . . O X X . |
$$ | . X O O X . . . O O O . X . X O X . . |
$$ | . X X O O O O . . X . . . X O . O . . |
$$ | . O X O . O X O . . . . X O O O O . . |
$$ | . X O O O X X X X , . . . X X O . . . |
$$ | X . X X O O X . . . . . . . . X O . . |
$$ | . X . . X X . X . . . . . . X . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ ---------------------------------------[/go]


Going back to black getting n18 and monkey jump black got 17 points beyond the triangles. So with these 3 gotes it went from black 17 to white 8 and black 4 ie black 13 to white 8 so difference of 21 or 7 points per move. 21 is close to 22. So seems they are about the same size :D (though that was with black possibly making a mistake to make L5 bigger than it really was to settle the ambiguous area).

I suppose there's also the meta-gaming aspect that any idiot 15 kyu up can see that n18 is a very big move, but l6 area is the kind of move you might miss the true size of, so if I want to bet on my opponent's lack of strength I could take n18 for myself and hope he doesn't see how valuable l6 is and then I can grab it later than I should if I assumed I was playing someone who will punish my mistakes.
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Offline Knotwilg
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #33 Posted: Thu Jan 02, 2020 9:35 am 
Oza
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While Uberdude was posting his analysis, I did mine: two difference games (attempts, I'm 15 kyu at it) and one Kata move analysis in 1 sgf.



Edit: I now realize they aren't really difference games :)


Last edited by Knotwilg on Fri Jan 03, 2020 1:42 am, edited 1 time in total.
This post by Knotwilg was liked by: Bill Spight
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Offline xela
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #34 Posted: Fri Jan 03, 2020 1:34 am 
Lives in gote

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While people are still thinking about Uberdude's and Knotwilg's analysis, here's another position from Shirae's book. This one is for reading, not counting, and I'm asking because I actually don't know the answer...

Click Here To Show Diagram Code
[go]$$Bc Black to steal lots of territory from white
$$-----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . X . . . . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


The book solution is a move that wasn't on my radar:
Click Here To Show Diagram Code
[go]$$Bc
$$-----------------------+
$$ . . . . . . 1 . . . . |
$$ . . . . . X b . a . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]

Stopping this incursion is tricky: it looks as though white has to fall back as far as a. There's a second diagram to demonstrate that :b1: at b is not so good.

But my question is: if black tries :b1: at one of these two alternative points, I can see that black is thin and there's more than one way for white to punish black, but what is white's best continuation?
Click Here To Show Diagram Code
[go]$$Bc Bad move number 1
$$-----------------------+
$$ . . . . . . . . . . . |
$$ . . . . . X . 1 . . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


Click Here To Show Diagram Code
[go]$$Bc bad move number 2
$$-----------------------+
$$ . . . . . . . 1 . . . |
$$ . . . . . X . . . . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


Last edited by xela on Fri Jan 03, 2020 4:03 am, edited 1 time in total.
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Offline Uberdude
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #35 Posted: Fri Jan 03, 2020 3:22 am 
Judan

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A complication in this one if the white group has spare eyes in the centre such that white can ignore black's move in the corner as a pure gote yose, then bad move 1 actually has a bigger followup than the 'correct' move, in that s18 next actually makes a few 1st line points for black and white can't make 1 eye in sente at q17.
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Offline jlt
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #36 Posted: Fri Jan 03, 2020 3:25 am 
Gosei
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There are so many variations, I don't know what the best response is but here is an attempt. If someone finds a mistake or a better response I would be interested.

Black can't play like this:

Click Here To Show Diagram Code
[go]$$B Bad move number 1
$$-----------------------+
$$ . . . . 0 9 3 . 5 . . |
$$ . . . . 6 X 2 1 4 . . |
$$ . X . X 7 8 O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


However, Black gets a ko by playing :b9: at :w10:. If Black can't fight the ko, he will play :b5: differently:

Click Here To Show Diagram Code
[go]$$B Bad move number 1
$$-----------------------+
$$ . . . . . c 3 5 6 . . |
$$ . . . . e X 2 1 4 . . |
$$ . X . X . d O a b . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]



Black can't tenuki, otherwise White captures with a-c-e.

If Black pushes at a, then the sequence b-c-d-e follows. In any case, whatever Black does, the sequence finishes in gote for Black.


Bad move 2: Black can't play like this:

Click Here To Show Diagram Code
[go]$$Bc bad move number 2
$$-----------------------+
$$ . . . . 0 9 2 1 5 . . |
$$ . . . . 6 X 3 4 . . . |
$$ . X . X 7 8 O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


...So must play :b5: differently...

Click Here To Show Diagram Code
[go]$$Bc bad move number 2
$$-----------------------+
$$ . . . . . 5 2 1 . . . |
$$ . . . . . X 3 4 6 . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]

Black can't continue like this:

Click Here To Show Diagram Code
[go]$$Bc bad move number 2
$$-----------------------+
$$ . . . . . 5 9 1 7 8 . |
$$ . . . . a X 3 4 6 0 . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


because it ends in gote: Black needs to protect, otherwise White can play at a.
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Offline Bill Spight
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #37 Posted: Fri Jan 03, 2020 3:34 am 
Honinbo

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xela wrote:
The book solution is a move that wasn't on my radar:
Click Here To Show Diagram Code
[go]$$Bc
$$-----------------------+
$$ . . . . . . 1 . . . . |
$$ . . . . . X b . a . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


Diagonal relationship! :)

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This post by Bill Spight was liked by: xela
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Offline xela
 Post subject: Re: Behind the scenes of some endgame tesuji
Post #38 Posted: Fri Jan 03, 2020 4:18 pm 
Lives in gote

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jlt wrote:
There are so many variations, I don't know what the best response is but here is an attempt. If someone finds a mistake or a better response I would be interested.

I had different move orders which I think come to the same result!

If black plays the one-space jump:
Click Here To Show Diagram Code
[go]$$Bc
$$-----------------------+
$$ . . . . a 7 3 . b . . |
$$ . . . . 4 X 2 1 8 . . |
$$ . X . X 5 6 O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]


I wonder if :w4: before :w8: is better move order, because if black wants to try the ko variation with black stones at a and b, then black has to make the ko shape at an earlier stage, allowing :w8: to be a local ko threat? But without the ko, it leads to the same end result.


If black plays the knight's move:
Click Here To Show Diagram Code
[go]$$Bc Black to steal lots of territory from white
$$-----------------------+
$$ . . . . . . 3 1 2 . . |
$$ . . . . a X b c 4 . . |
$$ . X . X . . O . . . . |
$$ . . . . . O . O O O . |
$$ . . . . . . . . X O . |
$$ . . . . . . . . X X . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |[/go]

Here, white a would be premature. But simply :w1:? The gap at a means that later, b and c will be sente for white. I think it leads to the same count as your variation: black has one less prisoner but one more point of territory. White has a 9-point corner, rather than 7 points after the book solution and follow-up moves.

This post by xela was liked by: jlt
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