Vital points

This friday a friend of mine came home and we spent the whole afternoon playing go, we used and abused of the clock, we killed groups, saved "unsaveable" groups and laughed a lot. But, above all, I put into the real world the concept of "vital point" and its value.

On the first game we played there was a situation like the following: Where is the vital point of this formation? what would you do as the black player?



My friend decided to go for the margin of the board, to expand himself a little bit assuming that his group would live. I had to chase him and finally stopped him from making more eyespace. He made a monkey jump elsewhere on the board, but he didn't fill the of this group. A monkey jump is up to 10 points, killing a group like this is much more valuable, so where is the vital point?

A vital point is a place to put the stone that makes you live unconditionally, it automatically creates two eyes and the group lives. Otherwise, if your enemy plays there, your group dies.

So here is the vital point:


For those who solved it and know the reason, the following explanation might be useless. There is another "problem" at the bottom of this post.

Why is that the vital point? Because it stops black from creating two eyes. There are some patterns you should see as soon as possible, as well as their vital points (they tend to be life-or-death problems, which can turn into win-or-lose). They are really worth it because they appear frequently on games and the one who finds it first will play it.

There are several patterns you'll find, like the L formation and so on (I'll make a post about that someday) but the easiest ones are these where you have to check the "eyespace shape" to see if it fits on one of these know patterns.

As you can see on the adjacent image, this are the forms you have to be familiar with, and their respective vital point.

How do I kill if I placed on the vital point?
You need to surround the enemy group, and once it's surrounded, start filling the eyespace with your stones in such a way that it always leads to one of the mentioned forms.
Once the enemy kills your stones (the ones inside his eyespace) play on the new vital point, re-fill and once he kills you, place on vital point... his eyespace will reduce to a 2 space eye, which you can kill with a snap-back.

As you can see on the situation above, we can assume that there is a semi-cross shape (in the adjacent column, the forth shape).

Here is another sample I found while watching some "Go teaching ladder" games. It was at the Iwamoto Tournament, in a game that involved Zwom (w) 12 kyu vs. Sylviainc (b) 8 kyu.
Try finding the vital point of the black group around D9. In this case there are two of them, due to "empty triangle" weakness of black.


You can enjoy the full problem interactive at Goproblems.com: Zwom vs. Sylviainc