Tewari Example 1

    Keywords: Joseki

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

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.

Velobici: please provide a link to the joseki move for White and the continuation.


Pairing stones  

The white+square 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.


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.

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 ?


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.

dnerra: Bill, I do not understand either how you can come to the conclusion that this exchange is almost equal. It makes the corner independently alive!

Possible continuation  

For example here white can cut at W3 with almost no worries -- a move that would be much more difficult to play without the marked stone, as then black could kill the corner by peeping at the same spot (in case he has good enough ko threats, which I know to be an unrealistic assumption at the moment). So the marked stone is a gain, and you have to compare that with how much worse W7 is compared to B6. That gets me really confused...

In summary, I agree that black is a little better off, but tewari doesn't help me much in arriving at that conclusion. And I think the loss is much less than half a move, in fact, I would happily pay it as komi if we were to have a game :)

Bill: Well, as I said, the two stones are roughly equivalent, given that the corner belongs to White. Since your critique does not make that assumption, I do not see that it really contradicts me in that regard. To be clear, perhaps I should have shown the position after the next two plays, but they are hardly determined. Besides, after W9 the damage is done.

Anyway, here is the position from one of the games.

Black sente  

After W2, White clearly owns the corner.

In addition, it is White's earlier protective plays in the corner that allow B1 to threaten to cut white+circle off.

White kikasare  

Here is a sequence without the two paired stones.

W10 is at best a middling yose. In addition, it fails to take the ko. At the start of the game, that is a loss of at least a half move. In addition, White seems to have been pushed around a little bit with the rest of the plays.

(Even if you play W10 at a, which has better aji, the above remarks apply.)

Joseki according to Kogo  

After this Black can start ko or exchange a for b. Pretty close to the original diagram on this page, suggesting that move 7 shouldn't be the one to blame, but move 9.

Bill: W7 comes in for criticism, given W9 at a, not per se. When tewari permutes the order of play, just because a play may be bad given one order of play does not mean that it was bad in the actual order. In fact, the culprit is frequently a later play that does not work well with a previous play or plays.

Tewari Example 1 last edited by Bill on December 4, 2005 - 20:44
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