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Yosu-Miru
    Keywords: Proverb

A probe (Japanese: yosu-miru) is a play made in order to see how the opponent reacts. After a probe, the opponent must choose between one of two or three options. You should have planned your game so that none of these options are beneficial to your opponent. -- Morten Pahle

Dieter Verhofstadt (1k) starts with a classic example of a probe given by Goran Siska and continues.

[Diagram]
Diag.: Possible answers for Black

Possible local answers for Black range from a to d. I'm less sure about d, so I'll discuss the other three here in more detail.


[Diagram]
Diag.: Block the probe from the outside

White crosscuts with 3 and plays kikashi with 5 and 7. Then White jumps out lightly with a, if this was a reducing manoeuver. Alternatively White leaves the situation for the moment and plays tenuki. Later in the game, the stones at 3, 5 and 7 will affect events at the top and center.


[Diagram]
Diag.: Reinforcing the outside

If Black thinks the outside is important, all outward aji will be removed by playing at 2. Naturally, this leaves the aji of White living in the corner with a. See the Tripod Group. With Black's territory reduced from the inside, White can now play a gentle reducing move, in case Black builds a moyo at the top.

Dave Sigaty: White may also push more aggressively at b. If Black answers at c, White plays a threatening to live with a better result than the tripod group. If Black answers instead at d, White plays c and escapes on the outside. This is discussed in The 1971 Honinbo Tournament, chapter 13.


[Diagram]
Diag.: Blocking the probe from the inside

Black 2 chooses to protect the corner. Either White continues with a, probably reverting to answer 1, or plays tenuki. The aji of 1 enables White now to invade deeper than if Black had answered with 2 at a.

Dave Sigaty: Another continuation for White is the clamp at b. In Strategic Concepts of Go Nagahara gives the continuation Black c, White d, Black a, and White e. By removing the stones at 1, 2, c, and b, Nagahara shows by tewari analysis that Black has played at a in answer to White's probe at d - an unfavorable exchange (in the position shown in the book).

Charles Matthews In fact the common answer from the pros to White now at a is Black at b. Black's capture is also played, but overall this seems to be another of those 'misconceptions' rife in this area.



Alain: The attachment under the kogeima shimari is often given as an example of a probing move. Here is another one which, I hope, will make the concept clearer.

[Diagram]
Diag.: An example in a "real game position"

Black 1 is an example of the yosu-miru technique. Before deciding how to continue the joseki on the lower left (a or b), Black probes White's intentions with 1.


[Diagram]
Diag.: Variation 1

If White plays at 2, Black will play 3 and 5. If Black had followed the joseki before playing at 1, White would have played at the marked point, aiming at the invasion point a. This does not mean that playing the joseki without exchanging 1 for 2 before is worse than playing 1 (it was played in numerous professional games). Black 1 is just a way to resist White's plan.



[Diagram]
Diag.: Variation 2

If White plays the large knight's move, Black plays this variation of the joseki and, again, White 2 is not ideally placed for invading at a.

-- Alain Wettach

Silly me, but what happens when White cuts? You could answer that Black can treat the stones lightly, but that's a fairly large gain for White locally anyway with the corner now secured. That's the only thing keeping me from studying and using this probe. -- lavalyn


[Diagram]
Diag.: White cuts

Charles Matthews The same question was asked on the intermediate plays page. This has happened at least three times in pro games: in a game Cho Chikun-Tozawa Akinobu 1977-05-26, and in games of Cho Hun-hyeon as Black. In each case I've seen, Black plays 3 as the double kakari, and White initiates a classic joseki by playing a or b. Clearly White already has taken a significant profit in the lower left corner. But it isn't easy to win the game with just one corner territory.



The Ultimate Yosu-miru?

[Diagram]
Diag.: Kitani 4p (white) vs Go 3p

June 1929 - This was the first meeting between Kitani Minoru and Go Seigen. Go had only been in Japan for a few months and reportedly had to ask around to find out if it was OK to start on tengen. His intention was to play manego which could be considered the ultimate yosu-miru technique - Black plays as shown and waits to see what White will play :-) Here is the continuation.

-- Dave Sigaty



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