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Kosumitsuke joseki
Path: DiagonalAttachmentPath   · Prev: DiagonalAttachmentAsInferiorShape   · Next: 44PointLowApproachDiagonalContactThenPincer
  Difficulty: Beginner   Keywords: Joseki, Question

There is a well-known pattern, occurring often in handicap games, which starts with a kosumi tsuke.

[Diagram]
Kosumitsuke pattern


There are several things worth noting:

  1. The kosumitsuke of B2 makes White heavy and is not an attacking move in itself. The attacking move is already in place, namely the BC handicap stone. This is in line with the proverb attack from a distance.
  2. The kosumitsuke of B2 doesn't protect the corner from an invasion. In fact, after the White stones have become strong, an invasion at a can be expected. B2 and B4 give some extra protection but no full security.
  3. The exchange B8 - W9 in particular must not be played automatically, but only if the area to the right of B6 and B8 is interesting and W9 doesn't lay waste to a more important area.
  4. A White move at b makes life, making miai of the two tiger shapes to form a second eye at the top.
This pattern occurs in only 6 pro games at Gobase, which is surprising given the enormous frequency with which it is played in amateur games, even non-handicap games.[1]

Let's have a closer look at the implications, with diagrams

[Diagram]
Generally bad

Here, the marked handicap stone in the previous diagram is absent. In this case B2 cannot in general gain an advantage: White becomes strengthened and the black corner isn't secure territory. (Charles). See also section (ii) of Joseki as a source of bad habits. (phenomene)



[Diagram]
Tenuki

The follow-up at a is not at all compulsory, either in amateur handicap or in even pro games. White will often tenuki and leave her options open, including b to d. A pincer to the right of the marked stone can also be expected.



[Diagram]
Attack

What happens if Black doesn't even grant White her shortest extension?


[Diagram]
Pattern

From pro play, where BC is mostly absent, we see that this sequence can be called a set pattern. B4 is a good empty triangle, denying White good shape. B6 covers his cutting point and W7 does likewise.


[Diagram]
Pattern

If B1 here instead of B4 in the previous diagram, White can cut and squeeze. Black 11 at a and Wite will protect her cutting point at b or c. This takes the fire out of the attack.


[Diagram]
Pattern

This is also seen, but there is a ladder issue. White denies the good empty triangle but ends up with a mediocre shape anyway.



Examples and counterexamples from pro play

DaveSigaty: Generally bad, hmmm... Rare I will grant you. But from time to time the duffers dust off this old chestnut! :-)

Note: Dave is responding to material that has been edited out, where the kosumi-tsuke is played when there is no previous hasami. --Bill

[Diagram]

Go Seigen - Hashimoto Utaro (Black) Ten Game Match in 1947


[Diagram]

Awaji Shuzo - Cho Chikun (Black) 3rd Kisei Preliminaries 1978-07-06


[Diagram]

Yi Ch'ang-ho - Yoda Norimoto (Black) 10th TV Asia Championship 1998-08-12


[Diagram]

Yu Ch'ang-hyeok - Ma Xiaochun (Black) 1st Toyota & Denso Cup 2002-03-19



[Diagram]
Shao-Dao

Shao Zhenzhong (B) against Cao Dayuan, Chinese team tournament, March 28, 1990.

It seems that professionals do in rare cases play this (pseudo-)joseki, typically when the player playing it is strong on the side. The idea is undoubtedly that a short extension (to a) is overconcentrated, but a longer extension like here leaves black open to an invasion and thus an attack. Prerequisite is that black is strong enough that this invasion must be considered important aji. - Andre Engels


Authors


March 2003: rewritten and rereferenced, rather than WME. A.o. material now to be found at BQM82. Dieter


[1] Bill: I'm surprised that the full pattern occurs that often in pro play. In a handicap game, how often will White play W7? Even if it is technically correct (honte), it seems too passive for a handicap game. In an even game, I would think that Black would have to be quite strong in the surrounding area for W7 to be right.

[Diagram]
Responding to the diagonal

Charles When Black attacks with BC the most common reply is W1 here. This gets White out into the centre and builds some influence. I can imagine White playing at a instead, for immediate life: that play is good for eye shape. But if White tries to live locally, Black at b becomes very good, to secure the corner while attacking. Therefore early in the game I'd expect W1 or something in that direction.


[Diagram]
Immediate cut

What about cutting immediately after the attachment? Guo Juan showed me this variation.



Charles Well, if she showed you, maybe you can show us? If W5 is played immediately, without a favourable ladder, it might be an overplay.



goantti A bit similar position occurs in the 1st Japan's Strongest Deciding Matches. Sakata Eio plays the cut against Go Seigen. Naturally white has the ladder.

[Diagram]
Immediate cut in a game 1

The white move 10 should be at A for good shape, but then black gets B.


[Diagram]
Immediate cut in a game 2

White lives in the corner, and next black plays around a to live on the side. In the game it was possible to exchange b for c before a.



In the Guo Juan -diagram a more severe pincer was possible, so the cut might work better than for Sakata (he eventually lost the game).



[Diagram]
Pro idea

This position has occurred in some pro games. The most common idea is this W1, to make some shape.



Well, one can guess that BC is played in cases where the contact play at the marked point would turn out to be an overplay.



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This is a copy of the living page "Kosumitsuke joseki" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.