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BQM41
   

[Diagram]
Diag.: Not joseki?

ChessWhiz: B2 is not joseki, as far as I can tell. How does white punish this move?

HolIgor: Let us see if black did not punish himself already.

The purpose of white 1 is usually a sacrifice in order to get a corner with an exit to one of the sides. So, let us see what happens if white enter san-san


[Diagram]
Diag.: Usual continuation

The question is now if the marked black stone is well positioned? In the usual joseki it is at 'a' or 'b'. In the latter case black needs one more move to cap the white stone. The marked stone does not seem to be placed very well as the eye making potential of the group would be, probably better with 'a'.


[Diagram]
Diag.: Another usual sequence

Now the black marked stone does not stop whites propagation along the top campared to a stone at 'a'.

It seems that a stone at 'a' is placed more efficiently. Of course, if this is not the firt corner joseki interration with other stones might change everyting.



dnerra: Hmm, that got me interested. HolIgor, maybe Black would deviate from the second joseki as below?

[Diagram]
Diag.: Black deviates from joseki

Despite the two weaknesses in his wall (a and b), I'd think this is good for Black.


[Diagram]
Diag.: Evil fighting

Of course, white might not cooperate, and then I will have a hard time showing that the Black 1 was not an overplay...


[Diagram]
Diag.:

I would start by claiming that I of course checked all ladders before playing the marked stone (B2 in the top diagram), and then see whether B1 here might be a tesuji.

And the fight continues beyond the scope of both this diagram and this analysis :-)


[Diagram]
Diag.: And another joseki deviation

Black could also play B1 here. I don't see a good move for Black 5 to fix the shape, however. Any shape guru to comment?

Yet under special circumstances, this could still be good for Black.


[Diagram]
Diag.: Create the shape defect immediately.

To come back to the original question: It looks very natural for me to start with W1 and W3. How should Black continue?



Nando: I've never seen this move before, so I checked [ext] gobase.org and, while it's rare, it doesn't seem to be unheard of in the professional practice. For instance :

[Diagram]
Diag.: Yu Ch'ang-hyeok 9-dan (B) vs. Mok Chin-seok 5-dan

To me, it looks like a "more" forceful move than the pincers A or B, and possibly making a better use of Black's wall in the bottom right.


[Diagram]
Diag.: Yu Ch'ang-hyeok 9-dan (B) vs. Mok Chin-seok 5-dan

White chose this sequence.

For the record, Black won by more than 10 points (the center moyo remained almost untouched, solidifying in a single huge territory)


I'd conclude that this move is playable under specific circumstances (looking at a couple other games with this pattern, I suspect that the plan is to emphasize an existing strength/influence on the side where the second stone is played and in the center)

(For those with access to Jansteen's site (not everyone?) the [ext] link to the game)


DaveSigaty: The Nihon Kiin's Igo Daijiten includes this move. The 1980 edition covers it with a total of 65(!) diagrams. A few of the key findings are shown below.

This is a non-standard move in modern Go but it is not a trick play. It is obviously outside oriented so if B can get extra value from a wall facing along the right or toward the bottom, it can be a viable choice. It appears in older Chinese games dating back to at least the 12th century AD.

[Diagram]
Diag.: Sort of joseki

Pulling back at 4 after W pushes through and cuts is one basic idea. However, it is too tame after challenging W with the fierce shoulder hit to start with. The result to 8 is judged better for W who has sente.


[Diagram]
Diag.: Quick but thin

B 1 and 3 here are a special strategy to keep sente in order to play down the left side. However, B is clearly thin and W threatens to start something with W "a", B "b", W "c" later.


[Diagram]
Diag.: Slow for W, interesting for B

If W switches to 7 here, it stops B from forcing W down as in the previous diagram but it is a slower approach for W. When B pushes at 8, W is unsatisfied after 9 because of B's good move at 10. However, if W plays 10 herself instead of 9, B will cut immediately at "a" and has interesting chances.


[Diagram]
Diag.: The center

B can try moving 4 to here but after 5 and 7 W is set to make a lot of territory in the corner. In the local situation W is better. However, as mentioned above, the original shoulder hit is usually based on the overall position so this may still work for B.


[Diagram]
Diag.: The top side

This 4 is more oriented specifically toward the top. Again however, B is going to have to cede the corner to W so locally this is going to hurt.


[Diagram]
Diag.: Locally

Locally the question seems to be what happens after B plays this combination of 4 and 6. The ladders toward the lower right need to favor B but if they do, this can lead to some heavy fighting that favors B at least as much as W.


[Diagram]
Diag.: Entering the corner 1

Playing into the corner is considered uninteresting. B's outside influence is too great after 8.


[Diagram]
Diag.: Entering the corner 2a

If 3 here, B will probably reply at 4. If 5 and 6 are exchanged, B will end with 10.


[Diagram]
Diag.: Entering the corner 2b

If 5 is here instead, B plays 8 and waits for the opportunity to play around "a", forcing W to respond in the corner.


ChessWhiz: Thank you, all, for your contributions.



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