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https://lifein19x19.com/viewtopic.php?p=247210#p247210Quote:
lightvector wrote:
Bill Spight wrote:
Playing a local sente with sente gains nothing, in terms of points.
For those who are confused about this detail - have you ever noticed that when pros or top amateurs estimate the score, they always pre-subtract out the sente pushes and other sente intrusions, even if the opponent hasn't played them yet? (See any number of online Go commentary videos, or if you've been to a Go club or Congress you may have seen strong dan players or pros do this in-person). Pretty much every strong amateur or pro that I've ever encountered counts this way.
That's because a very good "baseline" is that whenever a player has a clear sente move, they assume for estimation purposes that player will get it. So when that player actually does play that move in sente, there is no gain. Relative to that baseline, they have only gotten exactly what they already counted that player to get!
That's basically what "sente gains nothing" means.
Pio2001 wrote:
Even today, I feel confused, even about the modern "miai values". For example, when I compare a sente move with a value of 1 point and a gote one with a value of 20 points.
If I apply the traditional rule that says that a sente move is worth twice a gote move, and even if I use the modern "tally" calculation, all the theory says that the gote move is worth much more that the sente move, while it is obvious to anyone that it is better to play the sente first, in order to get both.
The simple answer is that you might be mistaken about what "modern" counting theory says
. There are TWO important values for locally-sente moves, not one - the reverse sente value (also known as the miai value, or the per-move gain), and the threat value - the
gain of the followup move if unanswered.
So let's say in your example the local-sente move has a reverse-sente value of 1 point and a threat value of 7 points. In that case, modern theory says to play it any time when the biggest moves elsewhere on the board are worth between 1 and 7 points. Ideally as late as possible to preserve ko threats, but definitely don't let it sit until moves elsewhere are all worth less than 1 point, then the opponent will be able to take it and you will lose out.
If you played it while there was a 20 point gote on the board, that would be a huge mistake, since the opponent would ignore it and take the 20 point gote. If on the other hand, the threat value was 30 points, then you could certainly play it now if you didn't mind using up the ko threat - in that case, theory would say to play it any time when moves elsewhere are worth between 1 and 30 points instead of 1 and 7 points. But you could also still wait, so long as there would still be other moves worth between 1 and 30 points after the 20-point gote was gone.
Does that make sense? (This is basically what Bill said, but restated in case a different way of wording it helps it stick).
Thanks for the explanations, lightvector.
Let's apply all this to the following example, White to play :
Attachment:
Endgame.png [ 12.38 KiB | Viewed 432 times ]
Two endgame moves are possible : A and B.
A is gote for Black and for White.
B is gote for Black and sente for White.
It is clear that the correct play is White G1 (sente), Black H1 (answer to White G1), then White A11 (gote).
If I follow the explanation of Robert Jasiek in his book Endgame 2 - Values, we have :
Upper left :Local count after Black A : 4 points
Local count after White A : 0 points
Local count as it is : (0+4)/2 = 2 points for Black
Tally : 2
Move value = (4-0)/2 =
2 points per excess move
Lower right :Local count after White G1 Black H1 : 15 points
Local count after Black G1 : 16 points
Local count as it is : 15 points
Tally : 1
Move value = (16-15)/1 =
1 point per excess movePage 115, Robert Jasiek writes :
Quote:
The moves in local gote, local sente, ordinary ko or ko threat endgames can be compared directly with each other by their move values.
And next :
Quote:
usually, play a move with the largest move value
Which gives the wrong sequence ! According to this, A should be played before B, because the move value is superior.
Mind that Robert makes a perfectly clear distinction between the move value and the move gain. Here, we are talking about the values, not the gains.
He even writes, page 62, that
Quote:
A gain may or may not be equal to the move value. If they are unequal, a gain improves our evaluation of a move. For example if a player starts his local sente sequence, but the opponent replies elsewhere on the board, the local value shift of counts is described by the gain of the player's local play rather than the move value.
In the next chapter, about Traditional endgame theory, the problem is the same. He writes, page 131 :
Quote:
Multiply by 2 the move value of playing in sente or reverse sente in a local sente to compare it with the move value of playing in a local gote
And, page 132 :
Quote:
After calibration, usually, play a move with the largest move value.
Here, A has a value of
4 points double gote, and B has a value of
1 point sente. Which means that A should be worth twice as much as B (4 vs 2). Again, wrong move order.
He then gives an example, page 134 example 3, where this exact method is applied... unfortunately, in that example, the gote move has a value of 7 points, and the sente one 4x2 points, which gives the right move order by accident !
But Robert is not alone. In his book "Yose, Fins de Partie au jeu de go", Dai Junfu makes the same mistake, although with a disclaimer about the inaccuracy of this method.
In "Rational Endgame, Antti Törmänen says, page 27, taking a sente move as an example, that
Quote:
[it] has no comparable points value at all. It simply enforces the expected outcome of the position.
So he avoids the mistake, but without giving an accurate method of comparison besides reading.
If I follow your explanations, lightvector, the correct calculation should use the "gain", as defined by Robert Jasiek, but move by move, as shown by Antti Törmänen (though Antti doesn't give the calculation, just the right move order). Robert Jasiek's book agrees with this (page 62), although he seems to have forgotten it 53 pages later.
In our example, we would have
Local count after White G1 = mean value between the two possible continuations :
Continuation Black H1 : local count = 15 points
Continuation White H1 : local count = -5 points
Mean value = (15+ (-5))/2 = Local count after White G1 = 5 points.
The answer Black H1 thus gains 15-5 = 10 points, while in the upper left corner, a move by Black gains 4-2 = 2 points.
Since the answer Black H1 is the move with the highest gain for Black, we can say that White G1 was sente (following Antti Törmänen's statement "Sente is relative to the whole board position" (p 27), which is what Robert Jasiek calls "global sente").
So we can still assume that the local count of the initial position in the bottom right is inherited from the result of the sente sequence, and is 15 points.
Now we can calculate the gain of White G1 : 5-15 = -10 points for Black, thus
10 points for White.
The gain of White A is easier to calculate :
2 points.
Now we can tell that the right move order is given by the decreasing gains :
Gain of White A : 2 points
Gain White B : 10 points
White must play B
Then Black has two choices :
Black answers B : 10 points
Black plays A : 2 points
Black must answer B with H1.