Life In 19x19

Hi,

If your opponent has a territory, and you have the opponent surrounded, then who's territory is it?
For example:

Black (X) and White (O) surround each other. Does this territory belong to black or to white, or does it need to be played out to decide who's territory it belongs to?

If it needs to be fought out, then why do opponents not always invade each other's territories to try and create eyes all the time. Why are territories ever left without a fight once they are surrounded. I have seen many games where I think I would continue fighting, but more experienced players don't?

Thanks
Regards
Craig.

I'm noob myself too, but i think it's simply becasue the better players had been in this situation many times before and/or can clearly see outcome of such attempt as an failure. I think for You it's just best to try it and see why it does or doesn't work.

Craig, all good questions.

jimmain wrote:If your opponent has a territory, and you have the opponent surrounded, then who's territory is it?

1. If the invader ( in your example) jumps in and kills B, then it becomes all W's territory.
2(a) If B can kill the invading W stones, AND B gets a life shape, then B keeps the territory as B's.
2(b) Even if B can kill the invading W stones, if B ends up with a dead shape, then it reverts to case (1) above.
3. If B and W end up as seki, it's more complicated -- depends on the seki shape.

jimmain wrote:or does it need to be played out to decide who's territory it belongs to?

More experienced playes will be able to tell whether the invader can live or die.
This is where lots and lots of Life-and-Death exercises and reading skills and experience enter the picture.

jimmain wrote:If it needs to be fought out, then why do opponents not always invade each other's territories to try and create eyes all the time.

Because some invasions are good and some are bad (for the invader). If the invasion is good for the invader, the invader invades. If not, then no.

jimmain wrote:Why are territories ever left without a fight once they are surrounded. I have seen many games where I think I would continue fighting, but more experienced players don't?

Because they already know the (likely) outcome of any invasions. At your level, if you are not sure, jump in and find out -- it's the best way for you right now: experiment, and find out for yourself.

First of all, you can see how to make a diagram here: viewtopic.php?p=1693&f=5#p1693

This makes it a bit easier to see what you mean

Click Here To Show Diagram Code

[go]$$
$$--------------
$$|O O O O . . . . . .
$$|X X X O O O . . . .
$$|. . X X X O O . . .
$$|. . . . X X O . . .
$$|. . . . X X O . . .
$$|. . . . X X O . . .
$$|. . . . X X O . . .
$$|X X X X X O O . . .
$$|O O O O O O . . . .
$$|. . . . . . . . . .
$$|. . . . . . . . . .
$$|[/go]

Black (X) and White (O) surround each other. Does this territory belong to black or to white, or does it need to be played out to decide who's territory it belongs to?

If it needs to be fought out, then why do opponents not always invade each other's territories to try and create eyes all the time. Why are territories ever left without a fight once they are surrounded. I have seen many games where I think I would continue fighting, but more experienced players don't?

Black is the one surrounding empty territory, so it belongs to black unless white can either:
a) create a living group in the empty area or
b) kill the black stones.

For white to create a living group, i.e., one with two eyes, inside that enclosed space is highly improbable because there is just not much room for him to do so and it should be fairly easy for black to prevent white from getting two eyes.

However, it is possible to imagine a situation in which white invades, black tries to kill him, but in the process removes too many of his own liberties resulting in either his death or a seki (where putting one's opponent in atari would put oneself in atari).

If white thinks he might have a chance at killing or getting a seki (in which neither player would get points in the enclosed area) he is welcome to try, and indeed a beginner can learn a lot by trying. More experienced players however recognize from their experience and their ability to read out a position whether an invasion is futile, so they don't bother.

Here, if white can prevent black from forming two eyes, he might have a shot. If you can't read that it's impossible, bombs away! Likewise for black - if he thinks white has a chance, he might prevent it by tossing in another stone for protection - but that makes his territory one point smaller, and if the invasion was doomed from the start and he loses the game by that one point, that will have been a big mistake!

P.S. Welcome to the forum!

jimmain wrote:Hi,

If your opponent has a territory, and you have the opponent surrounded, then who's territory is it?
For example:

Code: Select all

OOOO
XXXOOO
  XXXOO
    XXO
    XXO
    XXO
    XXO
XXXXXOO
OOOOOO

Black (X) and White (O) surround each other. Does this territory belong to black or to white, or does it need to be played out to decide who's territory it belongs to?

If it needs to be fought out, then why do opponents not always invade each other's territories to try and create eyes all the time. Why are territories ever left without a fight once they are surrounded. I have seen many games where I think I would continue fighting, but more experienced players don't?

Thanks
Regards
Craig.

When, as in your example, one player has surrounded points in a (currently) single eye, and the opponent has surrounded that player's group, and the opponent's surrounding stones are alive, how do you know whether that player's group is alive? That is an empirical question.

In your example the player's group is solidly connected, without a cutting point. Such groups have been extensively studied. The question is whether the opponent has an effective play inside the player's eye. Such a play is called an inside play, or nakade. (See http://senseis.xmp.net/?Nakade .) When there is one cutting point or more, whole books have been written on the subject.

If there is no cutting point and the eye has fewer than two points, the group is dead. If the eye has three points, the group is unsettled. The player with the move can live or kill. One rule of thumb is that if the eye has more than seven points, it is alive (with some exceptions). That does not mean that the opponent to move cannot make a seki. (Your example has many more than seven points in the eye, and Black is alive.)

As you are a beginner, I would suggest that you play by area scoring ( See http://senseis.xmp.net/?AreaScoring .), because then, after the dame stage, it does no harm to play inside your opponent's presumed territory.

Good luck!

Edit: P. S. A good study tool for these and other positions is Thomas Wolf's Go Tools ( http://lie.math.brocku.ca/GoTools/index.php .)

The game isn't over until you're certain, so play some moves in there and make black prove the area is his.

Conversely, if you are black, and you aren't sure you can kill anything white plays in there, add moves until you are sure. If your opponent is passing, he's saying he doesn't think he can live in there, and of course in that case you should agree with his cowardice and also pass.

jimmain wrote:Hi,

If your opponent has a territory, and you have the opponent surrounded, then who's territory is it?
For example:

Code: Select all

OOOO
XXXOOO
  XXXOO
    XXO
    XXO
    XXO
    XXO
XXXXXOO
OOOOOO

Black (X) and White (O) surround each other. Does this territory belong to black or to white, or does it need to be played out to decide who's territory it belongs to?

If it needs to be fought out, then why do opponents not always invade each other's territories to try and create eyes all the time. Why are territories ever left without a fight once they are surrounded. I have seen many games where I think I would continue fighting, but more experienced players don't?

Thanks
Regards
Craig.

People don't invade every opponent "terrritory" because the opponent might not respond so if the invasion doesn't succeed the invader loses points. When you are a beginner no one will object if you just invade to see what will happen, especially if you don't know yourself whether or not the invasion can succeed. But if you play invasions that obviously can't succeed some people would consider such invasions to be rude behavior.

Just to catalog some of the reasons people have mentioned for why *not* to invade:

1. If you're sure the invasion will die, invading would prolong the game unnecessarily.
2. If you're sure the invasion will die, you might not want your opponent to think that you didn't know that.
3. If you're sure that even if your opponent ignores your move and lets you play a second stone, the invasion will still die, invading just causes you to lose a point.
4. If you invade and the invasion dies, you'll have strengthened your opponent and lost your ability to reduce his territory from the outside.
5. If you're sure that the invasion will die, but that you opponent can't ignore your move, you want to save the invasion for a ko.

Note that reason -4- replies in reverse, too. Sometimes you don't want to wall off your opponent from the outside because that ruins your chances to invade and live inside.

This is the converse of your question, but: If you are behind and you will lose if you don't invade, you should close your eyes and invade. If there is zero chance, you can resign (but at your level, I'd think twice before deciding you don't have a chance).

When you want to invade, you have to keep in mind that you have to make a living group within your opponent's territory. The smallest living groups are shown on this diagram:

Click Here To Show Diagram Code

[go]$$
$$-------------------
$$|X . X . . . . X . X X . . . . . X X .|
$$|. X X . . . . X X . X . . . . . X . X|
$$|X X . . . . . . X X . . . . . . . X X|
$$|. . . . . . . . . . . . . . . . . . .|
$$|. . . . . . . . . . . . . . . . . . .|
$$|. . . . . . X X . . . . . X X . . . .|
$$|. . . . . . X . X X . . X X . X . . .|
$$|X X . . . . X X . X . . X . X X . . .|
$$|. X . . . . . . X X . . . X X . . . .|
$$|X X . . . . . . . . . . . . . . . . .|
$$|. X . . . . . . . . . . . . . . . . .|
$$|X X . . . . . . . . . . . . . . . . .|
$$|. . . . . . . . . . . . . . X X . . .|
$$|. . . . . . . X X X . . . . X . X . .|
$$|. . . . . . X X . X . . . . X X X . .|
$$|. . . . . . X . X . . . . . X . X . .|
$$|. . . . . . X X . . . . . . X X . . .|
$$|X X X X . . . . . . . . . . . . . . .|
$$|. X . X . . . . . . . . . . . . . . .|
$$ ---------------------------------------

$$|[/go]

In the corner you need at least six stones to live, at the edge eight and in the middle of the board you need at least ten stones.

Since you and your opponent set stones alternatively, you also have to keep in mind that he wants to prevent you from making two eyes for your invading group. That means that some weaknesses must exist in the phalanx of your opponent's surrounding stones. You have to exploit theses weaknesses by threatening something, e.g. atari some of his stones, connect to outside groups, cut off some of his stone in order to capture etc. This is a complex matter (for advanced players) where you would have to read out the situation deeply. There are tesuji for that purpose, so studying them would probably help you with that. As you are a beginner, I'd recommend what some people have already recommended: try it out yourself what works and what not.

Hi Everyone,

Thanks very much for all the great responses.
I understand the issues much better now, and realise that understanding whether or not white can invade and remain alive underpins everything.

I will continue to learn.

Cheers
Jim.

Simple question: Why on't I put a white stone into the black territory, so that it decreases from 18 to 17? If black wants to catch me, he has to put 4 stones around it and therefore loses four points. There must be something wrong with my thoughts, right?
Yes, I'm a beginner

Click Here To Show Diagram Code

[go]$$
$$--------------
$$|O O O O . . . . . .
$$|X X X O O O . . . .
$$|. . X X X O O . . .
$$|. . . . X X O . . .
$$|. O . . X X O . . .
$$|. . . . X X O . . .
$$|. . . . X X O . . .
$$|X X X X X O O . . .
$$|O O O O O O . . . .
$$|. . . . . . . . . .
$$|. . . . . . . . . .
$$|[/go]

This one stone is dead unless you manage to let him live.
It does not reduce your opponents points.

Sneegurd wrote:Simple question: Why on't I put a white stone into the black territory, so that it decreases from 18 to 17? If black wants to catch me, he has to put 4 stones around it and therefore loses four points.

It depends on a ruleset a bit (with chinese rules you don't lose points by playing inside your own territory, so this aspect is easier to grasp for beginners). Here black has to be careful not to end in seki, but generally if white plays in his territory, black can say (to himself) "no, you cannot kill me or make seki" and pass. If white continues, he can ignore until it threatens his life and then capture white. Notice that even then he doesn't need to physically capture every white stone, if they don't have chance to live / kill black. If white doesn't agree with him, they can play the situation out.