Double Sente

[RobertJasiek]

In "Yose question" viewtopic.php?f=15&t=11129 a few books have been mentioned that they would provide definitions of "double sente". What are those definitions? In First Fundamentals and Endgame 1 Fundamentals, I define:

"A local endgame is double sente if these conditions apply:
* A local sequence started by the player ends by the opponent.
* A local sequence started by the opponent ends by the player."

With this kind of definition, distinction from sente, reverse sente and gote is straightforward and consideration of double sente at all is meaningful. Since, on the surface, the definition is independent of values, problems of undefinedness do not arise. I wonder whether the other definitions are too miai-value-dependent to make sense. Bill suggests that double sente did not exist, but doesn't this depend on which definition one uses for which study purpose?

[Bill Spight]

In "Yose question" viewtopic.php?f=15&t=11129 a few books have been mentioned that they would provide definitions of "double sente". What are those definitions? In First Fundamentals and Endgame 1 Fundamentals, I define:

"A local endgame is double sente if these conditions apply:
* A local sequence started by the player ends by the opponent.
* A local sequence started by the opponent ends by the player."

With this kind of definition, distinction from sente, reverse sente and gote is straightforward and consideration of double sente at all is meaningful. Since, on the surface, the definition is independent of values, problems of undefinedness do not arise. I wonder whether the other definitions are too miai-value-dependent to make sense. Bill suggests that double sente did not exist, but doesn't this depend on which definition one uses for which study purpose?

OC, you can define double sente in this way. That does not mean that you can draw inferences about correct play or the value of a play or position. Nor can you use it to characterize or classify local positions.

[Bill Spight]

For instance, with that kind of definition for sente, we might have this:

$$B Initial position
$$ ------
$$ - . . .
$$ - X X .
$$ - . X .
$$ - . X .
$$ - O O O
$$ - . . .

Click Here To Show Diagram Code

[go]$$B Initial position
$$ ------
$$ - . . .
$$ - X X .
$$ - . X .
$$ - . X .
$$ - O O O
$$ - . . .[/go]

$$B Black plays first with gote
$$ ------
$$ - . . .
$$ - X X .
$$ - . X .
$$ - 1 X .
$$ - O O O
$$ - . . .

Click Here To Show Diagram Code

[go]$$B Black plays first with gote
$$ ------
$$ - . . .
$$ - X X .
$$ - . X .
$$ - 1 X .
$$ - O O O
$$ - . . .[/go]

$$W White plays first with sente
$$ ------
$$ - . . .
$$ - X X .
$$ - 2 X .
$$ - 1 X .
$$ - O O O
$$ - . . .

Click Here To Show Diagram Code

[go]$$W White plays first with sente
$$ ------
$$ - . . .
$$ - X X .
$$ - 2 X .
$$ - 1 X .
$$ - O O O
$$ - . . .[/go]

So we have a White sente, right?

Note that all moves are correct.

[RobertJasiek]

These kinds of definitions implicitly presume an understanding of 1) ending a sequence when no further valuable move or move with a value of similar size is available and 2) a choice of very meaningful (valuable) sequences among all available local sequences. Players are good at identifying and selecting such in nicely behaving local positions. However, the deeper one digs in an understanding of values and follow-up values and the more non-standard the behaviour becomes the more likely CGT-related thinking and definitions are motivated.

[DrStraw]

These kinds of definitions implicitly presume an understanding of 1) ending a sequence when no further valuable move or move with a value of similar size is available and 2) a choice of very meaningful (valuable) sequences among all available local sequences. Players are good at identifying and selecting such in nicely behaving local positions. However, the deeper one digs in an understanding of values and follow-up values and the more non-standard the behaviour becomes the more likely CGT-related thinking and definitions are motivated.

Hang on! In the thread which prompted this post you said that authors cannot make implicit assumptions. You cannot have it both ways.

[RobertJasiek]

Since currently a server error prevents me from reading all messages of that thread, I rely on my copy&paste storage of what I wrote:

"It is the responsibility of book authors to present correct examples instead of making dubious assumptions. [...] Since double sente depends on the (global) positional context, examples ignoring it must be accompanied by an explanation of the made simplifying assumptions"

In this, I did not write "authors cannot make implicit assumptions".

In fact, likely authors not writing pure mathematics have to make some implicit assumptions.

There is a big difference between making DUBIOUS assumptions versus making IMPLICIT (but not dubious) assumptions.

[tchan001]

Hang on, for a player who hasn't studied much about the endgame like myself, I'm not exactly one of those players who "are good at identifying and selecting such in nicely behaving local positions." I would normally rely on the accuracy of a book as giving the last word on how such a thing is suppose to behave when such a book is seeking to define something. A definition in my mind is something which I should be able to quote without fear of being retorted. When someone brings a counter example to my attention, then that casts doubt on the definition and suspicion on the rest of the work as I would worry whether I would lack the skills to identify and select in nicely behaving local positions as this is the assumption upon which the work rests. If I have problems with an assumption which places the burden of understanding on me as a SDK, I dread what happens if a DDK tries to read up on the subject as presented. Now if such a "definition" was presented as just a generalization, that would be a different matter.

Please note that I do enjoy RJ's body of works especially First Fundamentals. But just wanted to say that when I'm expected to operate by a definition, I expect the definition to be well constructed.

[RobertJasiek]

My definitions of double sente, sente, reverse sente and gote are well constructed because

1) the characterisation of double sente, sente, reverse sente and gote applies to all double sentes, sentes, reverse sentes and gotes, respectively,
2) none of the characterisations of one of double sente, sente, reverse sente and gote applies to any of the other of these terms and
3) the kind of characterisation provides exactly four definition variants for the four terms to be defined.

These definitions are insufficient for identifying related sequences and the types. Therefore, I also explain identification and verification of types for the ordinary players (instead of requiring value calculations). (And, of course, my examples are constructed properly.)

I am still wondering what the other books' definitions are. Do they offer (1), (2) and (3)?

[RobertJasiek]

The Endgame (Ogawa, Davies) "defines" as follows:

"Gote means gote for both sides, [i.e.] situations in which neither player could play in sente. [...]

[In] one-sided sente sitations, [...] one side has a sente move, but the other side has only a gote move. [...]

A reverse sente play is [...] the reverse of a sente play: one made by the gote side in a one-sided sente situation. [...]

A double sente situation is one in which either side can play in sente."

So the book "defines" gote, sente, reverse sente and sente by referring to gote and sente. Such are not definitions because the terms to be defined are used in the to-be-defined terms. However, at least the book relies on the good idea that one can define the terms by considering what either player can do. Let me improve on the book's attempt by redefining. I start with a moderate step, which still uses gote and sente to define the terms:

"A local situation is 'gote' if neither player could play in sente.

A local situation is sente if only one player can play in sente but the opponent can play only in gote.

A local situation is reverse sente if it is the reverse of a sente play: one player can play only in gote but the opponent can play in sente.

A local situation is double sente if either player can play in sente."

I have used consistent language to distinguish between 'local situation' and 'can play', to avoid the two words 'move' and 'play' for the same meaning, to avoid the less clear 'one side' and 'the other side' by using the clearer 'player' and 'opponent' (we are speaking of players, not of sides of the board), to avoid 'move' and 'play' to use 'can play' because the nature of a move is only given by how it can be played (in a sequence of moves) so that it turns out that a player ends with then having gote or sente.

Now, this is already pretty useful because gote / sente etc. for a local situation is distinguished from gote / sente for how a player can play. Still the latter awaits clarification: what does it mean that a player can play in gote / sente? And the answer is given as in my definitions.

Thus, while The Endgame (Ogawa, Davies) was on the right track, they stopped their definition attempts in an ambiguous state and failed to work out their idea properly.

Do the other books do any better?

[schawipp]

$$W White plays first with sente
$$ ------
$$ - . . .
$$ - X X .
$$ - 2 X .
$$ - 1 X .
$$ - O O O
$$ - . . .

Click Here To Show Diagram Code

[go]$$W White plays first with sente
$$ ------
$$ - . . .
$$ - X X .
$$ - 2 X .
$$ - 1 X .
$$ - O O O
$$ - . . .[/go]

So we have a White sente, right?

I would argue if that actually happened in a game then indeed the white move was sente. Sente generally only means that the opponent believes that he has to reply.

[Bill Spight]

Let me improve on the book's attempt by redefining. I start with a moderate step, which still uses gote and sente to define the terms:

"A local situation is 'gote' if neither player could play in sente.

A local situation is sente if only one player can play in sente but the opponent can play only in gote.

A local situation is reverse sente if it is the reverse of a sente play: one player can play only in gote but the opponent can play in sente.

A local situation is double sente if either player can play in sente."

With a proper understanding of "in sente" and "in gote", and the understanding that correct play is implied, these are perfectly good definitions for the contingent meanings of the terms.

Note that sente and reverse sente situations are the same.

[RobertJasiek]

Sente and reverse sente can, if necessary, be distinguished by specifying for whom they are it.

[Cassandra]

Sente and reverse sente can, if necessary, be distinguished by specifying for whom they are it.

The large Japanese Go Encyclopedia, already mentioned in the other "Yose" thread, does not explain "Gyaku Sente" in detail, but references to "Gyaku Yose" only.

Probably an impetus to think about the meaningfulness of using a term that contains "Sente", but is none (primarily) ?

[Bill Spight]

Is this a double sente?

$$B Double sente?
$$ ------
$$ | O X . X .
$$ | O X X X .
$$ | . X . X .
$$ | . O X X .
$$ | X O O O .
$$ | X O . O .
$$ | O O O . .
$$ | . O . . .
$$ | O O . . .
$$ | . . . . .

Click Here To Show Diagram Code

[go]$$B Double sente?
$$ ------
$$ | O X . X .
$$ | O X X X .
$$ | . X . X .
$$ | . O X X .
$$ | X O O O .
$$ | X O . O .
$$ | O O O . .
$$ | . O . . .
$$ | O O . . .
$$ | . . . . .[/go]

[RobertJasiek]

This inherently symmetric double sente can be delayed or not played.