hi everyone, new member here =) just trying to be good at Go while being a med student (which is hard!! )
so, I was reading The way of the moving horse by Janice Kim and I found this, I always have problems with invasions, I can't "see" if they are going to success (any link /book dealing with that would be great! =) )

Click Here To Show Diagram Code

[go]$$B 19x19 board
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . B . . . . . . . . X . . . . |
$$ | . . . O . . . . . O . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . T . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . O . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . O . . O . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

so I can't "see" why that invasion could be helpful (or in the triangle), to me W is only going to get stronger while B owuld struggle to live
any help with that?

You are right. But look at it from a different point of view. If black does not invade then white ends up with a huge territory. It sometimes necessary to take such risks in order to win the game. It doesn't mean you won't struggle when you do. But with experience you learn to avoid these positions in the first place.

_________________
Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

That is a rather strange position, it would be very unusual for that to appear in a higher-level game as white ought to add a move to the corner before all those centre moves. In that position there is one invasion that is very easy and no struggle to live: the 3-3 invasion under the 4-4. However that does let white get about 70 points on the outside (but black gets some too in the corner, and maybe retains sente) so you'd need to count if that low risk invasion is enough. One of the outside approaches is not so clear to live, white can more reasonably try to kill. If it does live then black potentially trashes more of the centre points, but that comes at the cost of a less clear way to make two eyes.

Click Here To Show Diagram Code

[go]$$B
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . O , O . . . . , . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 4 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . 5 . . X . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . 3 X . . . . . . . |
$$ | . . . X . . . . . X . 2 . . . , . . . |
$$ | . . . . . 6 . . . . 1 O . O . O . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

I happened to notice a position that reminded me a lot of this one (in Go World episode 35). 1933: Black is Go Seigen, White is Honinbo Shusai.

Click Here To Show Diagram Code

[go]$$W
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . O , O . . . . , . . . 8 . O X . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . X . . X . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . 2 . . . . X X . . . . . . . |
$$ | . . 6 X . . 4 . . X . O . . . , . . . |
$$ | . . 5 7 . 1 . . 3 . X O . O . O . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

White lives pretty comfortably in this game with a lot of points. White will go on to win by 2 points (in a no komi game)

Good question,

When you "invade", you usually want to do one of two things:

1-
Live inside, dealing a relatively large amount of damage

2-
Create forcing moves that reduce the territory faster.

Most cases, the aim is 1. Of course, the opponent will acquire some thickness on the outside, which means influence. You must invade at a time and place where the influence created by the adversary is:

1 Not very useful (stifled by your own *strong* stones)

2 Overconcentrated (in the diagram, white already had quite a bit pf influence and points in the area, and a reasonable amount of points, so invading at the san-san isn't as damaging as normal to black. The keima is sometimes used also, depending on the __WholE__ board position.

As for "seeing the future", you do want to be able to have some "awesome" reading skills up your sleeve, but by just doing many tsumego that you can solve in a minute, you'd naturally start finding possibilities in your games, by subconsciously recognising the shape. This is necessary, for even pros cannot always read everything that could possibly happen in some of the most hopelessely complicated positions, but make intutive jugdements of weather the invasion would work.

http://senseis.xmp.net/?OtakeHideovsChoChikun2ndMeijin

http://www.wbaduk.com/lecture/lecture_movie.asp

"Mediate" section has a very easy to follow invasion toturial.

ps: remeber that if the influence white gets is more valuable than the amount of territory you remove + the amount if territory you make, tgen the invasion was not succesful.

_________________
On Go proverbs:
"A fine Gotation is a diamond in the hand of a dan of wit and a pebble in the hand of a kyu" —Joseph Raux misquoted.

Nice example Polama; that was a famous unusual opening from Go Seigen. Shusai didn't invade at 3-3 because black would block to the right (he's undercut on the left side) and make a big solid territory in the middle and lower side.