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Tewari
Path: SequencingQuestions   · Prev: Timing   · Next: HowToLieWithTewari
    Keywords: Theory

There are two approaches to the concept of tewari.

  1. Take away an equal number of (superfluous) stones of both colors from a position. Then evaluate whether the remaining stones are working efficiently, in order to decide which side made the better moves.
  2. Invert or permute the order of moves, to see whether one would still have responded so that the actual position results. If this is not the case, that tells something about the previous moves.

Examples and opinions welcomed.

For limitations see how to lie with tewari.


Bill Spight: Here is an example from my recent play:

[Diagram]
Not joseki

In two games of mine all players were strong amateurs (U. S. 5-dan plus). In both games the play went the same through B10. White has deviated from joseki. Let's do a tewari analysis after W9.


[Diagram]
Pairing stones

The WS stone was played in response to a black stone at the marked point. Let's eliminate that stone (the black stone is already gone).
Now let's do the hypothetical replay.


[Diagram]
Replay

B6 at a would be joseki, but W7 is clearly bad. Taking the ko, or a, or even b would be better.



Very interesting. I've always wanted to discuss tewari: it is one of the relatively few concepts that approach our western flavour of analysis.

[Diagram]
Replay 2

Now, after the criticized move at W7, Black exchanges B8 for W9 (the "superfluous stones" that were removed). Isn't this a favourable exchange for White? In other words, how unfair have we been to White in criticizing her move, by removing two stones that perhaps weren't that equally superfluous. Or yet in other words, what are the opportunities Black lost with B8 for W9 in Replay 2, with respect to the opportunities White lost by playing W7 in both "replay" diagrams ?

--Dieter

Well, both B8 and W9 are poor moves at this point, but B8 does seem to be worse than W9. Tewari is not exact. You cannot always say that two plays are exactly equal, but often they are nearly so, and that is the case here. Under certain circumstances, depending on ko threats, W9 offers a little extra protection. But if we consider the corner to be White's territory, the difference between B8 and W9 is negligible.

If W9 were worth substantially more than B8, it would be because of the flaw at the marked point. But if White needed to protect that flaw, then W7 would not just be bad, it would be terrible! ;-)

Without tewari, we might think that White's play was OK. It solidified the corner and left Black without a clearly live group. But tewari shows us that, even given that B6 is somewhat doubtful and the pairing of the stones slightly favors Black, White has lost at least half a move.

-- Bill

I don't agree with your argument. In particular But if White needed to protect that flaw, then W7 would not be just bad, it would be terrible! ;-) - there's nothing bad about having to protect that flaw, given that it is going to be protected anyway. Andre Engels

Bill: Since the flaw is going to be protected anyway, the exchange of B8 and W9 is almost equal.



Authors:

DieterVerhofstadt
Bill Spight


Reinhardt: Since there is some argument about the usefulness of the above tewari analysis, I would like to try to provide an example that is more straight-forward.

[Diagram]
Black's response?

The question is how should Black respond to White's tsuke?

Let's examine Black a.


[Diagram]
Is this OK for Black?

The problem with B2 at a may not be readily apparent even from this position, but through a re-ordering of the moves I think it will become evident.


[Diagram]
Tenuki from a peep?

In this position, White peeps at W1 and Black ignores it, playing B2 elsewhere! There are only rare cases to ignore such a peep. If you do, this would allow White to push through, and if Black then plays B6, we end up with the same position as the previous diagram.

Any time you ignore a peep you can expect to get a worse position locally than if you had responded to it.[1] Therefore, through tewari analysis we can see that a was not the proper response for Black.


[Diagram]
A better way

Instead, B1 at c is a better response.

[1] phenomene : I think your analysis is not correct. Tewari analysis must proceed by removing the same number of stones for Black and White. Here all that you show is that in the second diagram, ignoring the peep and playing your sequence leads to the same result than in the first diagram, but this says nothing about the correctness of the play at a. Of course ignoring the peep in Diagram 2 is probably dubious, but in Diagram 1, Black has one less stone to begin with, so he shouldn't expect to get a result as good as if he answered the peep in Diagram 2. In other words, you don't provide a good reference to compare with.

With your kind of analysis, one can prove about anything. For instance, invading at the 3-3 point under a hoshi stone is not good, because if ones plays his first play in the corner at the 3-3 point, it is usually bad to tenuki on a shoulder hit approach!

Reinhardt: Thank you for pointing out my error in analysis. I stated incorrectly that if Black's response creates a result that is at all worse than the connection response to the peep, then the wrong move has been made. Even the diagram that I provided as a better response results in a less satisfactory position than connecting after the peep.

However, it can still be said that not responding to a peep results in a poor position locally, and since Black's response at a results in the same position as not responding to the peep, it is shown to be a poor position locally. The way that it has been shown is through a re-ordering of the moves. Here is a new diagram to make this more clear.


[Diagram]
Alternate diagram

This is the exact same as the Tenuki from a peep? diagram, except that the extra black stone is now B2. This diagram could be called Jump from a shoulder hit?. In any case, it creates the same position locally as a tenuki from a peep and thus is poor.[2]

What I tried to prove, but cannot, is that my better diagram is actually better. All I can show is that through tewari analysis, the move at a results in a poor position. It is up to you to decide if you can find a move that results in a better position. I happen to think that B2 at c in the initial diagram does.

I guess my example wasn't as straight forward as I had thought. (:

Let me extrapolate a bit further with another example of tewari analysis. Black's reasoning behind playing a may be expecting a certain White response.


[Diagram]
Black's wishful thinking

Maybe Black might expect White to pull back at W3. However, I think you can see that this is an unreasonable presumption even without a re-ordering of the moves.


[Diagram]
Thank you!

After re-ordering, we see that this position is the same as if White makes the shoulder hit at W1 and Black makes a knight's move underneath to get ahead. W3 is a classic example of a thank you move, and thus is not good. Therefore this position is not good regardless of what order it comes about.

So, going back to the original diagram, after White attaches, if Black plays a then White must block the connection instead of pulling back. Black's playing a expecting White to pull back is his error in judgment.

[2] phenomene : I think this is still not correct. B2 in answer to W1 is bad, but W1 is not a good move either: the correct move is W1 at W3. So we have to deal with a bad answer to a bad move: this tells one nothing (see how to lie with tewari on this).

Finally the sequence you criticize is a normal one and I doubt you can prove it to be bad by tewari. Your "better" diagram is not better, this is just a different global choice, and which one is best depends on the global position.



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This is a copy of the living page "Tewari" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.