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Tewari
   

I know two approaches to the concept of tewari. Probably only one of them is correct.

  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 the order of moves in order 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.


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

[Diagram]
Diag.: Fred seki

In two games of mine all players were strong amateurs (U. S. 5-dan plus). In both games the play went the same through B 10. White has deviated from joseki. Let's do a tewari analysis after W 9.


[Diagram]
Diag.: Pairing stones

The marked White 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]
Diag.: Replay

B 6 at 'a' would be joseki, but W 7 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 fewer concepts that approach our western flavour of analysis.

[Diagram]
Diag.: Replay 2

Now, after the criticized move at 7, Black exchanges 8 for 9 (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 wheren't that equally superfluous. Or yet in other words, what are the opportunities Black lost with 8 for 9 in Replay 2, with respect to the opportunities White lost by playing 7 in both "replay" diagrams ?

--Dieter

Well, both B 8 and W 9 are crummy moves at this point, but B 8 does seem to be worse than W 9. 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, W 9 offers a little extra protection. But if we consider the corner to be White territory, the difference between B 8 and W 9 is negligible.

If W 9 were worth substantially more than B 8, it would be because of the flaw at the marked point. But if White needed to protect that flaw, then W 7 would not be just 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 B 6 is somewhat doubtful and the pairing of the stones slightly favors Black, White has lost at least a half a move.

-- Bill



Authors:

DieterVerhofstadt
Bill Spight



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