Alguien wrote:
In the games I watch, played by very strong players, they never ignore leaning attacks, so they must be more urgent than how they look in my mind.
There is an element of selection bias here: if ignoring the leaning attack was a good move because the follow-up if ignored was not very big then they probably won't have leaned in the first place. It is quite possible that in the games of weaker players there will be inappropriate leanings in which tenuki is best.
As an example of this, here is a current OGS game of mine (I'm white,
http://www.online-go.com/games/board.php?boardID=347746). With 1 I jumped out with my 3 stones, trying to make shape for sabaki in black's area. Black 2 is a sort of leaning attack: if I ignore it r7 is rather annoying. However, a more typical leaning attack would be the contact move of q6: as it touches my stone it takes a liberty so is a lot harder to tenuki. I considered tenuki-ing p6 to help my centre group but in the end decided to take profit at q8, daring black to do his worse. Black then leaned again at p8 and I decided to ignore and help my group run and make shape at l8 and so on. Black did get some profit from 10 (I blocked at r7, he ataris at q9 and I connect), but I don't think this was so big for black and white gained from this exchange.
- Click Here To Show Diagram Code
[go]$$Wc Ignoring the lean
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . X X O X X X X . . . . X O . . . . |
$$ | . . X O O X O O . . X . . X X O O O . |
$$ | . . X O . O . . O , . . . . . X X O . |
$$ | . X X O . . . . . . . . . . X . X X X |
$$ | . O X X O O . . . . . . . . . . O O X |
$$ | . O O X X X O . . . . . . . . . . O O |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . . O X . . . . . . . . . . . . . . |
$$ | . . . O X . . . . , 9 . . . . , O . . |
$$ | . . . O X . . . 6 . . . . . . . . . . |
$$ | . . O X . . X . . . 5 . . . 4 3 . . . |
$$ | . . O X . . X O . . . . . . . 0 . . . |
$$ | . . O . . . . O . . 1 . . . 2 . O . . |
$$ | . . . . . X X O . . . 7 . . . . . . . |
$$ | . . . O O O O X X , . . . X . X X O . |
$$ | . . . . O X X . . X . 8 . . . X O O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Instead of leaning at 4 I think black should maybe have played at l8 himself as this combines a cap with attacking my shape (it aims at the k6 cut). If white runs out at j6 then black k7 cuts something off.
- Click Here To Show Diagram Code
[go]$$Wc Attack first
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . X X O X X X X . . . . X O . . . . |
$$ | . . X O O X O O . . X . . X X O O O . |
$$ | . . X O . O . . O , . . . . . X X O . |
$$ | . X X O . . . . . . . . . . X . X X X |
$$ | . O X X O O . . . . . . . . . . O O X |
$$ | . O O X X X O . . . . . . . . . . O O |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . . O X . . . . . . . . . . . . . . |
$$ | . . . O X . . . . , . . . . . , O . . |
$$ | . . . O X . . . . . . . . . . . . . . |
$$ | . . O X . . X . . . 4 . . . . 3 . . . |
$$ | . . O X . . X O . . . . . . . . . . . |
$$ | . . O . . . . O . . 1 . . . 2 . O . . |
$$ | . . . . . X X O . . . . . . . . . . . |
$$ | . . . O O O O X X , . . . X . X X O . |
$$ | . . . . O X X . . X . . . . . X O O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
There is also an element of fighting spirit at play. If you ignore the lean to secure your group then you lose elsewhere from ignoring the lean. Maybe you save your group but you lost too many points so you lose the game from playing such a compromise. If you answer the leaning and it is still not 100% clear your group is dead then you are gambling on surviving the attack after the lean, with the cash in the bank from answering the leaning so you might have a 50% chance of losing by resignation versus a 95% chance of losing by 10 points.
Alguien wrote:
If one uses a leaning attack to build strength to attack another group, the leaning attack itself must be bigger than the other group's death or it should be ignored to save the original group.
Indeed, but in Go, unlike in life, death is not always certain. Using another OGS game of mine to illustrate, this time I was black and the one doing the leaning. With 1 I leaned on the k3 stone and white answered all my moves. I pushed white on the 4th line, something you usually don't want to do, giving him a lot of territory. This cut off the central group in sente, which I then capped at 7. I remember at the time I was rather surprised white answered my leaning, I thought it was very risky for white and his central group would very likely die. In the game (which was rather exciting!
http://www.online-go.com/games/board.php?boardID=317813) I did manage to kill it 80 moves later but it was harder than I expected.
- Click Here To Show Diagram Code
[go]$$B Lean then kill?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . O X . . . . . . . . . . . . . |
$$ | . . . . O X . . . . . . . . . . . . . |
$$ | . . . O . . . . . X . . . . . X . . . |
$$ | . . . . . X . . . . . . . . . . . . . |
$$ | . . O . O O X . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . X . X . . . . . . 7 . . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . O . O . X . , O . . O . X O . . |
$$ | . . . . . . . . . X . . . . X O O . . |
$$ | . . . . . . . . . X O O . . X X O . . |
$$ | . . . . . . . . . X X O . . . . O . . |
$$ | . . . . . . . . . . O O O . X . . . . |
$$ | . . . O . . . . 5 3 . X . . . . O O . |
$$ | . . . , . . . 6 2 1 . . . . . X X X . |
$$ | . . . O . . . . . O 4 . . X . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Alguien wrote:
I need to see how to profit, not from a working leaning attack and the continuing main chase but from an ignored leaning attack.
What I expected when I leaned was that white would have to tenuki to save the central group, resulting in the compromise as below. It should be fairly obvious where my profit is on the lower side. I don't know why white answered the lean, maybe he underestimated the danger to the central group, maybe he was motivated by fighting spirit. Quite probably he was influenced by the fact we have played 20 games together and I have won 19 (but some very close) so if he goes for a simple compromise it is pretty much certain that I will win the game by a small margin. A better way to increase the chances he wins the game is to take the money on the lower side and gamble the result of the game on a huge tsumego.
- Click Here To Show Diagram Code
[go]$$B Compromise
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . O X . . . . . . . . . . . . . |
$$ | . . . . O X . . . . . . . . . . . . . |
$$ | . . . O . . . . . X . . . . . X . . . |
$$ | . . . . . X . . . . . . . . . . . . . |
$$ | . . O . O O X . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . X . X . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . O . O . X . , O . . O . X O . . |
$$ | . . . . . . . . . X . . . . X O O . . |
$$ | . . . . . . . . . X O O . . X X O . . |
$$ | . . . . . . . . . X X O . . . . O . . |
$$ | . . . . . . . 4 . 2 O O O . X . . . . |
$$ | . . . O . . . . . . . X . . . . O O . |
$$ | . . . , . . . . . 1 . . . . . X X X . |
$$ | . . . O . . . . 3 O 5 . . X . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]