Six Kyu Noseki

Alex Weldon: On IGS, with Black, I usually play the Manchurian Fuseki. Since it involves a 5-4 point, I need to know my 5-4 point joseki. But, I've discovered, my opponents, at the 6k* level, don't.

People usually play the 3-4 point, rather than the other option, at 3-3. At first, I almost always played the keima press, with the continuation shown here:

5-4 point knight's move press joseki  

But then, one time, I was playing against an opponent who played the 5-4 point, and instead of playing the press that I used to favor, or attaching at a, he attached on the outside, at b. I played what seemed intuitive for me, and it ended up with a very bad result. I checked Essential Joseki, and indeed, the play that was "intuitive" for me turns out not to be there, meaning that it's probably wrong (although Essential Joseki is, of course, far from being a complete listing of all joseki).

Since the wrong play seemed, at first glance, to be sensible to me, I reasoned, perhaps it would seem to be reasonable to my opponents. And indeed, my opponents play the wrong move more than 50% of the time at the 6k* level, allowing me to reap unreasonable advantage by playing the outside attachment.

Here's the mistake:

The wrong response  

It looks good at first ^[1], because White is expecting this continuation, which gives White big territory in the corner, and Black outside influence in the wrong direction (since his choice of that 5-4 point should generally indicate that he was going for influence down the left side, not the top):

White's fanciful imagination  

Really, though, Black plays a two-step hane, trapping White in the corner.

Noseki  

Even if White a, Black b, White c, Black d, White's corner is just 12 points, while Black's outside influence is considerable. has some aji, but if White plays the hane and connect a and c, Black could always play d at e instead to remove that aji, in return for allowing White the possibility of an endgame clamp at f. Or, he could use to capture , at the expense of his left side influence.

My opponents don't always even play this well, sometimes descending with at instead of cutting, in which case Black can play at , threatening a lethal cut one line above .

This is the usual response to the outside attachment:

Joseki  

Next, Black will continue with a if he wants influence on the top side (giving White a ponnuki in the corner), or at b if he wants to exchange for the corner (giving White a ponnuki on the outside).

Noseki  

There's more to this noseki. If White plays to to capture a stone, Black sets up two ladders (double threat ladder-maker).

No ladder  

If in the previous diagram is played at the marked spot, there is no ladder. (Pointed out by Charles)

Noseki  

If the center ladder doesn't work, he sacrifices two stones and gets the better of it in terms of influence.

Noseki  

If White lures out her cutting stones, Black starts a ladder at and White has to defend at . Normally, Black should not fear being cut this way, but if the surrounding area greatly favours White, he may also choose for the previous diagram.

Dieter

The wrong response  

May I point out that "it looks good at first" violates basic technique. Permitting a hane at the head should always look bad at first, then maybe be playable, like in the avalanche joseki. See also joseki as a source of bad habits. --Dieter

Professional play  

Checking my game collection, I found that this has actually been played a few times among professionals.

Out of over 20,000 games in the MasterGo database, the position occurs 182 times, of which is played 4 times (2%). However, in all those cases White had some support down the left side and cut with here to start a fight.

However, this position also occurs after another sequence:

Black 1 breaks a ladder  

namely here as a ladder breaker, against .

We are supposing is elsewhere takes/removes ladder. This follow-up with might be played a little later.

This gives two games where the hane is played:

Game example 1  

Ushinohama Satsuo (W) - Wu Songsheng, China-Japan Go Exchange 1978

Continuation  

Game example 2  

Cho Chikun (W) - Kato Masao, Judan match 1988.

Shortly afterwards, Black exchanged Black a-White b-Black c-White d. - Andre Engels