Cross Cut Example 3

Cross-cut position from a teaching game by Minue  

Now, before I start arrogantly misusing modern AI to critique the advice of a much stronger player than me, I'll make a couple of general remarks:

• Minue is writing in the context of beginners trying to navigate a 9-stone game and trying to learn the basics of good shape. If you're black in a high handicap game, often the move which settles your shape and keeps you out of trouble is better than the move which starts a complicated fight (which you theoretically win provided you don't make any mistakes later). This is true both for your chances of winning the current game, and as a foundation for future learning. So in this context, I'd take Minue's advice over KataGo's. (See also: The Psychology of Handicap Games at L19.)
• But what if you're playing an even game and looking to improve your fighting skills? I'm looking at this because the proverb cross-cut - extend! is one of the most misleading proverbs out there (although cross-cut - atari everything in sight without thinking isn't any better). Where KataGo's suggestions differ from Minue's, I think they point to a couple of principles that can help in crosscut fights.

So the challenge in any crosscut situation is that, at first glance, there are eight candidate moves. It's a lot to choose from.

Black's options  

You can extend from either stone (a-d), or you can atari either stone (e-h). Exercise for the reader: only one of these is truly awful. Which one? Hint: see Haengma tutorial for beginners/Ja Choong Soo.

Of the other options, KataGo has a clear top three, but the remaining moves are just small mistakes, not game-losing blunders (at least not for us amateurs). I don't know of a systematic way to rule out the inferior moves; to some extent you just have to read out all the continuations, and to some extent you hone your intution by seeing lots of examples.

Here I'm going to analyse three continuations:

• Extending at c is "very questionable" according to Minue, but KataGo's second choice.
• Extending at a is Minue's recommendation, but not one of KataGo's top three!
• Atari at e is KataGo's top choice.

I'll leave out the atari at h, KataGo's third choice, because this article is already going to be too long.

Variation c, the good extension

Not so questionable...  

Here, white has the option of squeezing like this. Next, should black play a or b? I've seen shape problems that look quite similar.

Classic good shape; at  

In other contexts, you'd recommend this . Unfortunately it allows squeezing black into a dumpling. But it leaves a cutting point at a for later. This is often the lesser evil. If you try to prevent the squeeze:

Often not a great idea?  

White descends at , and black will need to capture at a anyway. Then white has a solid wall on the outside. Allowing this can be worse than making the dumpling.

But wait! In the "good shape" version, is an atari and black has to capture immediately. In the other variation, the stones still have two liberties. This is significant.

KataGo's improvement  

Before capturing at a, black has time to throw in the cut at . If white pulls out of atari, then is a liability later on. If white doesn't pull out of atari, then black doesn't need to play a after all. Either way, this makes a big difference to the evaluation of the position.

Lesson 1: Sometimes an extra tempo is worth more than stylish shape.

Variation a: the other extension isn't as good as it first looks

White has other options  

Here, white can atari at , threatening to capture . After , white's only options are a or b. In either case, the cutting point at c is a serious weakness, and black can squeeze. See if you can work out the details, then look up the answers at Haengma tutorial for beginners/Cross-cut position.

But white has another option. I can't see a general principle at work here: I think you just need to read it out.

Nice try, but this isn't it.  

First I wondered if white could avoid the squeeze by playing here. Well yes, there is no squeeze, but white's left with three heavy stones that are in a lot of trouble. White can do much better.

White's refutation  

White just needs to atari underneath with , sacrificing . Both sides get to make a settled shape. Given that white was outnumbered locally in the starting position, this is a very good result for white.

Variation e: the good atari

Now we get to KataGo's recommended move:

What next?  

How do you follow up here? Beginner's instincts might be to play a or b, to capture and strengthen . But instead:

A variation on the first variation  

Remember at the top of the page, where black played at ? And in that case, white's best reply is at a. Well, after the exchange of for , white at a now looks like a bad move. So instead:

Lots of choices for both  

White's best option is to play , capturing . After , KataGo likes all of a, b and c about equally well, and black can choose whether to follow up by capturing or by attacking the weak white stones below. So this is definitely the sort of wide open position that you don't want as black in a handicap game! But for an even-game fight between players of equal strength, black is looking good here.

The key move is the combination of and : after giving atari, you don't need to defend the stone or go all-out trying to capture .

Lesson 2: Treat atari as a forcing move and be prepared to sacrifice that stone

(Aside: I'm sure I remember being told that abandon forcing stones? is a fundamental proverb, but we don't seem to have a page for it?)

Discussion welcome. I bet there's things I've misinterpreted, or other variations I should have mentioned.