I'm just playing the sequence I posted earlier, so there's not much to say about that, but I think I should probably have explained more about the decision to invade in the first place, because recognising the value of these seemingly tiny invasions is something that I used to really struggle with.
It comes down to a concept that is at the heart of go: Exchanges. One of the first things I read when returning to go after a 2 year break was the sensei's library page on
ippoji. It completely changed the way I thought when playing the game because I used to think of invasions as basically just profit. i.e The invader takes territory that would have belonged to the other player, and they are either successful and live, or the other player fights them off and they die. Now I realise that they are much more complicated than that.
The most obvious example is the 3-3 invasion of a 4-4 stone. I'm sure everyone knows that the invader takes territory while the invadee (my spell-checker says that's not a word but it should be so I'm leaving it in
) builds thickness. A direct invasion is usually considered a bad ides, so let's say they play joseki like below:
- Click Here To Show Diagram Code
[go]B Corner
$$ ------------------
$$ | . . . . . . . . .
$$ | . . O O X . . . .
$$ | . . O X X O . X .
$$ | . . O X . . . . .
$$ | . . . X . . . . .
$$ | . . O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]
Black exchanged the corner for the side, and the pros say the result is about equal, so how much was the invasion worth? If black gained exactly as much as white did, then the value of the invasion was 0 points. Obviously it depends on the whole board situation, and it's much better than letting black take the whole lot (maybe that means not invading is worth -5 points(random number) or invading is worth +5 points), but because both players profit from almost any invasion, the actual value of most invasions is surprisingly small.
I think this is one reason why pro games are often so close, but it's all too easy to create a situation in which one player stands to gain much more from an invasion than the other. This is why, when trying to make territory, I aways ask myself "what do I get if my opponent invades here". If the answer is f@#k all in gote, then it's a very bad move, because then your opponent's invasion becomes worth a lot more. Let's go back to a 3-3 invasion of a 4-4 stone. This is a pretty extreme example, but it's the kind of situation that does crop up in games I play (which probably says awful things about my playing).
- Click Here To Show Diagram Code
[go]B Corner
$$ ------------------
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . a . . . . X O
$$ | . . . X . . . X O
$$ | . . . . . . . X O
$$ | . . . . . . . X O
$$ | . . . X . . X O .
$$ | . . . . . . X O .
$$ | . . . . . . X O .[/go]
How much is an invasion at "a" worth here? It's worth a huge amount for two reasons.
1) Any thickness black builds is useless, so any territory white makes is pure profit.
2) With another stone black claims the area as his territory, so every stone played/everything white surrounds is a loss for black.
With that in mind, let's count it. (I can't be bothered to work out a proper sequence since I'm just trying to make a general point, so forgive me if this is incorrect)
- Click Here To Show Diagram Code
[go]B Corner
$$ ------------------
$$ | . . . O O X . . .
$$ | . O O O X X . . .
$$ | . . O X X . . X O
$$ | O O O X . . . X O
$$ | X O X . . . . X O
$$ | X X X . . . . X O
$$ | . . . X . . X O .
$$ | . . . . . . X O .
$$ | . . . . . . X O .[/go]
White makes 6 points of territory.
White plays 10 stones.
Black plays 10 stones.
So black loses 26 points and white gains 6, making the total value of the invasion 32 points, which is huge by any standard, but is especially impressive if you compare it to other invasions worth only a few points.
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Splatted
(Edit: I guess that's not so surprising when you've already seen that I've tenukid)
was a mistake...
