In the Game

This concept seems easy to understand and to apply into real games, but constantly I find these blunders on my games against other players and on others games.
The basic example is a response to a 3-3 invasion, you always ask yourself: where should I block? The answer is: on the one with the biggest size and the one with most probabilities of turning into your points at the end of the game.

But it also applies to middlegame fights and cuts.

If white now played on J5, what would you do?

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.

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.

We all have heard something like: "try doing double purpose moves". And, sometimes, we wonder how to do it. Dual purpose moves are made in such a way that they achieve 2 purposes (obviously), the most obvious one is to make territory or strengthen yourself while attacking a weak group from the opponent.

Yesterday I saw an interesting game on KGS between a 10k and a 11k, there was an interesting fighting early in the game which went to the center and involved one big group of each player.
All of a sudden, when the black player realises that his E9 group is alive, he decides to play from the other side. This is the result, starting at move 71:


As you can see, black managed to build a nice wall on the N column just by attacking and trying to close white. The marked wall is incredibly valuable in terms of points, though it doesn't turn everything into territory (invasion around R5 is still possible) it makes a huge influence on the marked spots.

And, minutes later black player did almost the same on the upper left corner:


As you can see, white started on R14, black pincered, white went for the corner and the following movements are more-or-less traditional response for 3-3 invasion. So, as a result, black got another wall facing his moyo (huge now) which works perfectly with his R12 stone.

If you haven't yet checked, try invading black's moyo. There isn't any obvious available invading point, as they both deffended for invasions on E17 (first white) and R5 (then Black), which surprised me quite considerably, because I expected white to invade on R5 before letting black deffend.

Here is the game if you are interested on it.
There are mistakes from both players (some of them are big ones), so don't study it, but I wanted to show you this nice sample of "dual purpose" moves.










By the way, one of them asked me not to say his name, so that's why I changed the usernames.