It is currently Tue Apr 16, 2024 4:52 pm

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 71 posts ]  Go to page Previous  1, 2, 3, 4  Next
Author Message
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #21 Posted: Sat Dec 06, 2014 12:40 pm 
Lives in sente

Posts: 757
Liked others: 114
Was liked: 916
Rank: maybe 2d
I apologize in advance if my commenting here confuses things, and also to Bill if he was intending to present things in different way. Here's my attempt at an overview.

There are two main notions involved in what Bill is describing:

The "count" or "value" of a local position:.
This is obtained by assuming that all locally sente sequences are played and responded to, and taking the average when playing is locally gote for both sides. This also applies recursively - for example, if in a double gote situation one of the moves has a later sente followup, when we compute the value for it to be averaged, we assume the player who played it also gets the sente followup after that. This is roughly what many strong players do when they want to estimate a territory but cannot read out everything - tentatively assume sente moves are played with sente, split the difference on gote.

So in a simple one sided-sente position, the value of the position is equal to the value after the sente move or sequence is played and responded to. In a double-gote position, the value is the average of the two possible values after the gote sequences by each player (and recursively if there are further followups thereafter).

The "temperature" or "urgency" of a local position, or what spending a move "gains" in that position:
This is simply how much you change the value above by taking gote in a position - what you gain by investing your turn. (A sente sequence gains nothing since we're already assuming sente is played and responded to). So if playing is locally gote for at least one player, then the urgency is the difference between the value of the current position and the value after that player plays the gote move or sequence. If neither player's playing is locally gote, that is, if both are locally sente, then the the urgency is zero (see below for why zero makes sense).

So in a simple one-sided sente position the urgency is the difference between the value after the sente sequence is played and responded to, and the value after the reverse sente is played. In a double-gote position, the urgency is the half the difference of the possible values after each player plays (which again are computed recursively).

Other Terminology:
A move is locally gote for a player if playing it decreases the urgency of the position.
A move is locally sente for a player if playing it increases the urgency of the position.
A move or sequence of moves gains a certain number of points for a player if playing that sequence changes the value of the position in favor of that player by that many points.

A note: a bunch of the above may appear circular as stated - value and urgency are defined using gote and sente, and gote and sente are defined using value and urgency. But it's not too hard to make it non-circular. You define things inductively/recursively, where given a game tree you begin with the leaves and gradually work your way up the tree assigning values and urgencies as you go, so that you never actually circularly depend on anything. I actually haven't seen the exact full procedure laid out anywhere for computing these values, but in the process of reading what's on Sensei's library and from Bill's posts (and based on what makes mathematical sense), I think I've reverse-engineered the algorithm. I can try to post it for the math-minded if anyone is are interested.

Note that locally gote and locally sente refer to the idea of "urgency" here, rather than a comparison of how many points appear to be made secure by the move versus the threat/followup it enables (some people's intuitions more closely adhere to the latter notion). With these particular definitions, double-sente generally can't happen. In any situation that one would want to call double-sente, although responding to the sente move by either side might be huge and urgent, playing a move in the original position is also extremely urgent. So urgent in fact that for at least one player, the act of playing the supposed double-sente move in the original position will not cause the urgency to rise any further, but rather to lower.

The only time playing is locally sente for both players, as defined above, is when the moves fail to gain points, or even lose points, as in the following. This is why we define the urgency to be zero if both players playing is locally sente.
A is locally sente for black and B for white, because they both raise the urgency of playing in that area. But despite making a threat these moves don't actually gain anything overall. C is locally sente for both players for the same reasons - it raises the urgency of another play in the area, but is a losing sente for both.
Click Here To Show Diagram Code
[go]$$c
$$ -----------------------------
$$ . . X a O b O . O X . O X . .
$$ . X . X X O . O O X c O X . .
$$ X X X O O O O O X X O O X X X
$$ . . . . . . . O O O X X X . .
$$ . . . . . . . . . . . . . . .[/go]


Any locally double-sente positions are usually just variations on these kinds of positions where except for zero-net-value cleanup exchanges and dame moves, the positions are all already finished.

Other comments:
This counting system does extremely well at putting endgame moves on a single numeric scale such that always playing the move with the highest number (urgency) is close to optimal. In some sense, it is the unique best way, up to scaling, of doing so. Which means that if you play a good endgame, you likely have learned to evaluate and rank endgame moves by something quite close to Bill's particular notion of what moves "gain", even if you don't consciously do so.

Lastly, why is Bill adamant on resisting the idea of the the second-line diagonal as a double sente?

Here's my understanding. Usually either:
* It's so urgent that it will be played almost immediately after the position itself forms. Then, it's closer to being part of the local tactics that generated that position, as opposed to an endgame move that remains on the board to be played later at an appropriate time.

* Or else one side, say Black, threatens significantly more than the other. In this case, it's locally sente for Black and locally gote for White. Then conditional on the move actually staying on the board for a little while, thinking of it as Black's sente is also usually correct globally. Why? Assuming it was correct for the move to remain unplayed so far, White's threat must not be large enough relative to other moves to make it forcing. So Black will likely get to play it with sente, because he can play it any time his own threat has become large enough to make it forcing but where White's threat hasn't.

* Or else both sides threaten about the same amount, such as when the position is nearly symmetric. In this case, it's large but locally gote for both sides. Then conditional on the move staying on the board for a while, large double gote is also a good way to think about the move globally. It will likely be played right around when it becomes the biggest/most urgent move remaining. Since the response to it is a few points less urgent than the move itself, it will often not be responded to immediately or at all. Which is what happens not-infrequently in pro games, consistent with it being gote. Even if it is responded to, that's no different than if there were two separate large gotes on the board, one of them a few points less than the other, but both larger than other moves. One player gets the larger one, then the other player gets the smaller one.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #22 Posted: Sat Dec 06, 2014 1:15 pm 
Judan

Posts: 6725
Location: Cambridge, UK
Liked others: 436
Was liked: 3719
Rank: UK 4 dan
KGS: Uberdude 4d
OGS: Uberdude 7d
Just as an aside I was surprised when Bill showed such a small position as his 2nd line kosumi. I assumed it was more like this one (where the teritorrial loss from tenuki is far bigger (and very hard to count), nevermind the eyespace implications):

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


or
Click Here To Show Diagram Code
[go]$$W
$$ . . . . X . O . . . .
$$ . . . . X , O . . . .
$$ . . . . X . O . . . .
$$ . . . . . 1 . . . . .
$$ . . . . . . . . . . .
$$ ---------------------[/go]


Edit: Ooops, I missed out some of this thread with my reduced posts per page setting to avoid errors, so I see this point (except my surprise) has been made already.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #23 Posted: Sat Dec 06, 2014 3:14 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
John Fairbairn wrote:
6. I dispute that there is a proverb "sente gains nothing". That is just a western joke.


It is neither Western nor a joke. If (local) sente gained any points, then the calculation of the size of gyaku yose as the difference between the value of the result after the gyaku yose and the value after the sente sequence would be wrong. Also, if (local) sente gained any points, then assuming that local sente are played when estimating the value of the whole board would be wrong.


Quote:
7. With various usages of sente washing around, should we not try to get away from the term "reverse sente"? I am sure the Japanese avoid it for good reason.


Japanese is sometimes more logical than English. Darn those inscrutable Occidentals, anyway. :mrgreen:

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #24 Posted: Sat Dec 06, 2014 3:19 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
Uberdude wrote:
Just as an aside I was surprised when Bill showed such a small position as his 2nd line kosumi.


That was Kano's mistake, not mine.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #25 Posted: Sat Dec 06, 2014 3:33 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
John Fairbairn wrote:
Quote:
The Kano examples are double hane-connects, but one is a 7 point sente and one is a 20 point gote. :) Neither are local double sente. The 20 point gote is very likely to be global sente, but the 7 point sente is not.


Sorry to harp on these points to do with Kano, but is it not the case that in practical terms he is correct? According to Ishida's book on counting, moves in the fuseki are typically worth something like 25 points.


Sorry, the 20 points is Absolute Counting (TM). Ishida uses deiri counting, so divide by 2 to compare the two. The 20 point gote is likely to be a (global) double sente at almost any time. As for the 7 point sente, the sente threat is 17 points by Absolute Counting, so Black can play the sente at almost any time. However, the threat for White after the gyaku sente is only 3 points by Absolute Counting. That means that if White should make the play, it will almost certainly not be sente, no matter how White may maneuver.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #26 Posted: Sat Dec 06, 2014 3:54 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
Click Here To Show Diagram Code
[go]$$W Diagram 3 Gote
$$ -------------------
$$ . . O . . O O . O . X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


This is a gote position. How can we tell?

Click Here To Show Diagram Code
[go]$$W White first
$$ -------------------
$$ . . O C . O O 1 O . X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


If White plays first, the local result is -1 (1 point for White).

Click Here To Show Diagram Code
[go]$$B Black first - A
$$ -------------------
$$ . . O . . O O 1 O . X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


Click Here To Show Diagram Code
[go]$$B Black first, White second - B
$$ -------------------
$$ . . O C 2 O O 1 W C X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


If Black plays first and later White plays second, the local result is +2.

Click Here To Show Diagram Code
[go]$$B Black first and last - C
$$ -------------------
$$ . . O . 3 O W 1 W C X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


If Black plays first and later second as well, the local result is +6.

Click Here To Show Diagram Code
[go]$$B Black first - A
$$ -------------------
$$ . . O . . O O 1 O . X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


So the value of the result after :b1: is +4, and the next play gains 2 points.

Click Here To Show Diagram Code
[go]$$W Diagram 3 Gote
$$ -------------------
$$ . . O . . O O . O . X . .
$$ . . O O O X X X X X X . .
$$ . . . . . . . . . . . . .[/go]


As a gote, the original position is worth 1.5 points, and a play gains 2.5 points. Since the White reply gains only 2 points, this is indeed a gote.

In a real game, since the difference between 2.5 points and 2 points is only 0.5 points, it is possible that Black will be able to make a play with sente. But this is a local gote. :)

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #27 Posted: Sat Dec 06, 2014 11:22 pm 
Judan

Posts: 6131
Liked others: 0
Was liked: 786
lightvector wrote:
I can try to post it for the math-minded if anyone is are interested.


Of course:)

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #28 Posted: Sun Dec 07, 2014 1:07 am 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
For the math minded. :)

Given this game, { a || b | c }, a > b > c, to find the temperature, t, solve a - t = max(b, (b+c)/2 + t).

The mean value of the game is max(b, (2a+b+c)/4).

The temperature of the game is min(a-b, (2a-b-c)/4).

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #29 Posted: Sun Dec 07, 2014 8:39 am 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
More for the mathematically inclined :)

Given the game, {a | b || c | d}, a > b > c > d,

To find the temperature of the game, solve

min((a+b)/2 - t, b) = max(c, (c+d)/2 + t)

The mean value of the game is the middle value of b, c, and (a+b+c+d)/4.

If (a+b+c+d)/4 > b, the game is a Black sente.

If b > (a+b+c+d)/4 > c, the game is gote.

If c > (a+b+c+d)/4, the game is a White sente.

Note that in no case is it double sente.

The game, {a | b || b | c}, a > b > c, equals b. (In go, ko considerations may invalidate that equality by destroying the independence of the position.)


Edited for clarity. :)

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.


This post by Bill Spight was liked by: drmwc
Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #30 Posted: Sun Dec 07, 2014 10:13 am 
Dies with sente
User avatar

Posts: 109
Location: Boston
Liked others: 159
Was liked: 19
Rank: AGA 1k
KGS: sligocki
Online playing schedule: Ad hoc
Bill Spight wrote:
For the math minded. :)

Given this game, { a || b | c }, a > b > c, to find the temperature, t, solve a - t = max(b, (b+c)/2 + t).

The mean value of the game is max(b, (2a+b+c)/4).

The temperature of the game is min(a-b, (2a-b-c)/4).


I find follow, could you explain your notation?
What does { a || b | c } mean?

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #31 Posted: Sun Dec 07, 2014 11:33 am 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
Shawn Ligocki wrote:
Bill Spight wrote:
For the math minded. :)

Given this game, { a || b | c }, a > b > c, to find the temperature, t, solve a - t = max(b, (b+c)/2 + t).

The mean value of the game is max(b, (2a+b+c)/4).

The temperature of the game is min(a-b, (2a-b-c)/4).


I find follow, could you explain your notation?
What does { a || b | c } mean?


Sorry. It means from the original position, designated by ||, Black can move to a position worth a (for Black), and White can move to game {b | c}. In that game Black can move to a position worth b and White can move to a position worth c.

¿Es claro? :)

Edit:

For the position in the diagram a couple of notes back, the game looks like this:

{6 | 2 || -1}

The mean value is min(2, (6 + 2 - 2)/4) = min(2, 1.5) = 1.5. It is gote.

For the sente diagrammed in note #2, the game looks like this:

{9 || 8 | 0}

The mean value is max(8, (18 + 8 + 0)/4) = max(8, 6.5) = 8. It is sente.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #32 Posted: Mon Dec 08, 2014 10:28 am 
Lives in gote
User avatar

Posts: 452
Liked others: 74
Was liked: 100
Rank: 4 Dan European
On a side note, in one of the earlier diagrams the monkey jump is not as good as the one point jump. 4 is better than 3.

Click Here To Show Diagram Code
[go]$$B White has a fighting chance.
$$ ---------------------------------------
$$ | . . . . . . 3 . . . . . . . . . . . . |
$$ | . . . . . . . . . 1 . . . . . . . . . |
$$ | . . O . . . . . O . X . . . . . X . . |
$$ | . . . , . . . . O , X . . . . , . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | O O O O O O O O O , X X X X X X X X X |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . . . . . . O . X . . . . . . . . |
$$ | . . . , . . . . O , X . . . . , . . . |
$$ | . . O . . . . . O . X . . . . . X . . |
$$ | . . . . . . . . . 2 . 4 . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #33 Posted: Mon Dec 08, 2014 11:31 am 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
About criticizing Japanese texts, and Kano in particular.

I criticize the Japanese texts because that's what I read. I have only a few go books in English, not including The Endgame. One Japanese text that I do not criticize is O Meien's recent book. He does not talk about double sente because he does not need to. In the future I hope that he criticizes how other texts treat double sente as local.

Kano's Yose Dictionary is one of a set of books including, among others, the Fuseki Dictionary, the Ko Dictionary, and the Handicap Go Dictionary. I bought several of those books in the summer of 1975. To the best of my knowledge, Kano is the first writer to raise questions about local double sente. I speculate that he took the job of writing a comprehensive yose dictionary quite seriously, and that he wanted to explain why certain local positions, such as the three examples I have shown in recent threads, were double sente. He ran into problems, and, in the case of the 7 point sente, came up with the idea of necessity to explain why White was more likely to reply than Black. In the case of the "two point double sente" I suspect that his ghost writer came up with the example and Kano, who believed in local double sente like everybody else, checked the diagrams under the assumption that the double kosumi is double sente, and verified that the difference in results was two points, and then moved on.

I know from my own experience how easy it is, when you are trying to come up with an example to illustrate a point about go, not to stop and think about other aspects of the example, such as how you would actually play it. :) I do not for one second think that, had it come up in a real game, Kano would have answered the kosumi or considered it sente for either player.

In 1974 all the writers about yose believed in local double sente. Kano had the thoroughness to come up with some bad examples. He also recognized that there was a problem. Without Kano I am not sure that we would have had O Meien. :)

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #34 Posted: Mon Dec 08, 2014 11:59 am 
Judan

Posts: 6131
Liked others: 0
Was liked: 786
Not every text treats local double sente with the implied pretence of it also being a global double sente. Besides, local double sente is an abstraction because it avoids consideration of a player having the turn. Instead, like in CGT diagrams, one can assume that EITHER player might have the turn.

What is the contents of Kano's yose and ko dictionaries?

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #35 Posted: Mon Dec 08, 2014 12:47 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
RobertJasiek wrote:
What is the contents of Kano's yose and ko dictionaries?


Sorry if I was unclear. The dictionaries had different authors. Murashima Yoshinori wrote the Ko Dictionary. All of the dictionaries were fairly encyclopedic. :)

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #36 Posted: Mon Dec 08, 2014 12:59 pm 
Lives in gote

Posts: 553
Liked others: 61
Was liked: 250
Rank: AGA 5 dan
Click Here To Show Diagram Code
[go]$$ Value = 6.5 or 8 ???
$$ -------------------
$$ . . O . . O X . . .
$$ . . O X X O X X . .
$$ . . O O X O O X . .
$$ . . . . X X X X . .
$$ . . . . . . . . . .
$$ . . . . . . . . . .[/go]


If the first W move is gote, and if we assign probability 1/2 to either player later getting the next play, then this position is worth 6.5 points for B and the first W move is worth 2.5 points. This calculation gives me some clue when to make the play in a real game.

If the first W move is sente, meaning we assign probability 1 to B getting the next play, then this position is worth 8 points for B, and the first W move is worth 0 points. This gives me no clue when to make the play in a real game. If I evaluate this instead as "W one point sente (or B one point reverse-sente)", then I have the information I need to guide my play.

The value of 0 for the sente move seems like a meaningless tautology. If the value of the initial position is calculated assuming the sente sequence with no branches, then the value of the end position is back-assigned to the starting position. So of course the move under consideration does not change the calculated value of the position.

It seems rather arbitrary to alter the probabilities of the branches of the decision tree this way. First assign probablilty 1/2 to each branch, then evaluate the value of each intermediate position, then evaluate the value of each intermediate move, then reset the probabilities of some branches to 1, then reevaluate the values of the intermediate positions, then reevaluate the values of the intermediate moves. It seems like the rule is to reset the branch probability if the branch creates a move worth more than the previous move? That might be a reasonable guideline, but nothing more. Why not for example assign probability 3/4 to some branch, if I feel that the followup is moderately large?

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #37 Posted: Mon Dec 08, 2014 1:31 pm 
Lives in gote

Posts: 553
Liked others: 61
Was liked: 250
Rank: AGA 5 dan
lightvector wrote:
Or else both sides threaten about the same amount, such as when the position is nearly symmetric. In this case, it's large but locally gote for both sides.
Here "locally gote" is a mathematical definition, related to your counting method, not necessarily a guide to proper play. In a real game, I would contend that such positions are quite often truly double sente (given the global board position), and players try hard to get the first play. If I think to myself "this move creates a large followup, probably larger than anything else likely to be on the board, so I will consider it sente", then I am injecting some global board evaluation into the equation, and it seems like I could improve the evaluation and my play.

lightvector wrote:
Even if it is responded to, that's no different than if there were two separate large gotes on the board, one of them a few points less than the other, but both larger than other moves. One player gets the larger one, then the other player gets the smaller one.
Surely there can be great practical real game value in making the move that sets up this situation. But in your counting method, the more followup value created by the first move, the less value you assign to it, with the extreme limit being an absolute sente move valued at zero.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #38 Posted: Mon Dec 08, 2014 1:52 pm 
Oza

Posts: 3655
Liked others: 20
Was liked: 4629
I remain unconvinced by Bill on Kano. For the avoidance of doubt, I am not saying Bill's way of counting boundary plays is in any way flawed (nor am I able to say whether it useful or correct).

But my feeling is that Kano is being criticised for something he never said or intended. I have to stress it's a feeling, as I'm not qualified to dilate on the mathematics, but it's a strong feeling, and it's based on the following observations.

First and foremost the idea of double sente has been around since at least Shi Dingan referred to it in the Qing dynasty, and it is alive and kicking today in each of the oriental go-playing countries. Kano sticks to his guns in the 1985 edition of his book, and although it's a different example he still uses a large-scale one where the value of the respective sente moves is very different.

The huge Chinese "Practical Comprehensive Manual of Go" of 1997 gives an example with a totally different position but likewise a huge discrepancy in the value of the two sentes. One allows killing of a group if unanswered, the other just allows a non-fatal incursion, i.e. the same idea as in Kano's big 1974 example. Yang Jinhua and Wang Qun also give examples in Chinese, large and small scale, in all cases with different values for each side's plays.

The Taiwanese author Li Song gives examples, too, and also has a good introduction on the history of boundary plays going back to Guo Bailing, i.e. early 17th century.

I'll skip Korean examples, as I think the picture is clear enough: we have had in place a method of talking about boundary plays for centuries. It beggars belief that if this was flawed, someone - even if he had to be a genius like Go Seigen - would not have mentioned it. It's true we had quirks like people not noticing a Shusaku game had been miscounted until an amateur queried, or weird positions that previous rules couldn't cope with. We've even had Kano himself, as I recall the story, exposed by Matthew Macfadyen for a mistake in an endgame problem, much to Kano's embarrassment. But these are quirks and one-offs - double sente plays occur in every game, multiple times.

So has Bill defied the odds? Maybe, and the novelty of CGT gives some grounds for believing in a platform for new insights. But as with conspiracy theories, I always think Occam's Razor is a better tool.

I believe the Oriental usage of double sente is nothing more than a description, that works in the same rough-and ready way that I say my wife's dress is red but accept she may call it burgundy, cherry, salmon, fuchsia, etc. (and in the way of the world I have accept I'm wrong while knowing I'm right enough). In contrast, while Bill will have to speak for himself as to exactly what he means by double sente, what comes over to me is that he sees it as a cog in a mechanism, and if that cog isn't exactly machined the whole mechanism will grind to a halt. Great if he can do it, but it's hardly fair to Kano and the others to blame them for non-working cogs.

That reminds me of one of my favourite stories. A Japanese interpreter was working with a group of American senators in Japan. The Japanese side referred to something as the honmono, the genuine article. Keen to show his prowess, the interpreter decided to translate this as "the real McCoy". Whereupon a senator excitedly interjected, "Say, you know Scotland too? My family comes from there!" Faced with expectant Japanese faces the interpreter felt obliged to render this straight into Japanese. Result, baffled faces and muttering of "How the hell did Scotland come into this?"

My view is that, presented with the alleged mistake, Kano's reaction would be "How the hell did cogs come into this?"

If I'm right and the Oriental view of the term is purely descriptive, we still have to assume the description is made for a purpose. The main answer to that seems to be differentiate double sente from one-sided sente and double gote, the categories universal in the Oriental texts (some add reverse sente, others treat it as a sub-category), and to point out that, no other things being problematical, double sentes are played first. Implicit in that, of course, is an addition to the description of who has sente. Imagine the situation in the aforementioned 20-point + 7-point double sente at which Bill took umbrage where one side has an area large enough not to have its life affected, but where that position arises only because that side has just made a move to create that area. Obviously he has gote. Just as obviously the other side will grab the sente. As he plays it he will perhaps think of it only as sente play, but if he was given that position cold and told he had sente, and he wants to know where to play, it is useful to be able, descriptively, to give general advice along the lines of "give priority to double sentes".

That's a trite example, no doubt, although I think it is always implied in the Japanese that it will be known in each case which side it is to play, and RJ seems to be saying that this is not necessarily assumed in western methodology.

In practice, pros seem to operate more on the crude but practical lines sketched out by Uberdude, much as we can see in Genan's Igo Shukairoku. Moves are mostly categorised as X points gote and X points sente, while double sentes are taken for granted and reverse sentes require a slurp of tea or a cup of coffee. But pros differ from amateurs in two main ways. One is that they have memorised counts for large numbers of standard boundary positions, and the other is that they stress restraint in the timing of boundary plays, to ensure that full account is taken of all aji (either to use it or eliminate it), so that many sente plays we amateurs make are far too early for a pro's taste - pun intended :) That seems to be the only way pros incorporate the concepts of local and global, and as far as I can recall, they have never used these specific terms.

I am very unsure about this, but I think it might be correct to say that pros have a bipartite approach. They make an overall count of territory and prospective territory and then decide on a strategy. Quite separately, they calculate the values of boundary plays as X-points sente or gote and thus decide on a move. In contrast, western researchers appear to me to be looking for a method that can integrate these two parts.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #39 Posted: Mon Dec 08, 2014 2:23 pm 
Honinbo

Posts: 10905
Liked others: 3651
Was liked: 3374
mitsun wrote:
Click Here To Show Diagram Code
[go]$$ Value = 6.5 or 8 ???
$$ -------------------
$$ . . O . . O X . . .
$$ . . O X X O X X . .
$$ . . O O X O O X . .
$$ . . . . X X X X . .
$$ . . . . . . . . . .
$$ . . . . . . . . . .[/go]


If the first W move is gote, and if we assign probability 1/2 to either player later getting the next play, then this position is worth 6.5 points for B and the first W move is worth 2.5 points. This calculation gives me some clue when to make the play in a real game.


Yup. It tells you that the time for either Black or White to make a play here is when other plays on the board gain around 2.5 points. Do you believe that? ;)

Quote:
If the first W move is sente, meaning we assign probability 1 to B getting the next play, then this position is worth 8 points for B, and the first W move is worth 0 points.


Err, no. The sente exchange, :w1: - :b2: (not shown), gains zero points. But that just means that each move in the exchange gains the same number of points.

Quote:
This gives me no clue when to make the play in a real game.


But if you ask yourself how much the Black response in the sente exchange gains, you find out that it gains 4 points. This tells you that when other plays on the board gain less than 4 points, White is likely to be able to make the play with sente. :)

Quote:
If I evaluate this instead as "W one point sente (or B one point reverse-sente)", then I have the information I need to guide my play.


What do you mean, instead?

Quote:
It seems rather arbitrary to alter the probabilities of the branches of the decision tree this way. First assign probablilty 1/2 to each branch, then evaluate the value of each intermediate position, then evaluate the value of each intermediate move, then reset the probabilities of some branches to 1, then reevaluate the values of the intermediate positions, then reevaluate the values of the intermediate moves. It seems like the rule is to reset the branch probability if the branch creates a move worth more than the previous move? That might be a reasonable guideline, but nothing more. Why not for example assign probability 3/4 to some branch, if I feel that the followup is moderately large?


The argument given here is not a proof. For proof, try the method of multiples. Set up a number of copies of this position and play them out, both with Black playing first and with White playing first. You will see that the average result converges to 8 points for Black. :)

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Top
 Profile  
 
Offline
 Post subject: Re: How to tell if a play or position is sente
Post #40 Posted: Mon Dec 08, 2014 3:08 pm 
Lives in gote

Posts: 553
Liked others: 61
Was liked: 250
Rank: AGA 5 dan
Bill Spight wrote:
mitsun wrote:
If the first W move is sente, meaning we assign probability 1 to B getting the next play, then this position is worth 8 points for B, and the first W move is worth 0 points.

Err, no. The sente exchange, :w1: - :b2: (not shown), gains zero points. But that just means that each move in the exchange gains the same number of points.

Ah, I get it now. The first move in the sente sequence converts an 8-point position into a 4-point position, then the forced response converts it back into an 8-point position. The 8-point initial value depends on evaluating the overall sequence as sente, but the 4-point intermediate value assumes double gote at that point. Despite all this, I have the feeling you are not comfortable saying that the first move is sente and has a value of 4 points?

It seems like I still need to recall the "sente" qualifier to know that I should play this fairly urgently as W, and I need to recall that the response is worth 4 points in order to know more precisely when to play it. Without your counting method, I would consider this as one point sente for W, to remind me that taking this point is pretty much my privilege, and I would need to recall that the threatened followup is worth 8 points, in order to know more precisely when to play it. Maybe not so much difference after all.


Last edited by mitsun on Mon Dec 08, 2014 3:11 pm, edited 1 time in total.
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 71 posts ]  Go to page Previous  1, 2, 3, 4  Next

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group