Life In 19x19

A lot of the 'I capture 2 (or 3 or 4), you capture 1' positions are totally different with this rule.

Passive ko sounds interesting. I think that both it, and Tibetan ko, could be used with beginners.

Click Here To Show Diagram Code

[go]$$Wc
$$ ------------------
$$ | 1 O O 2 X O . . .
$$ | X X X X X O . . .
$$ | O O O O O O . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

So this is how I understand the situation. White makes the internal atari play, Black takes.

Click Here To Show Diagram Code

[go]$$Wc
$$ ------------------
$$ | S S S 2 X O . . .
$$ | X X X X X O . . .
$$ | O O O O O O . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . 3 . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

White now cannot break the eyespace, so plays a ladder breaker as a ko threat. Black can answer the threat, or he can live.

1) If there are two to three moves ruled out by this, then there will be several times as many places where the best play is different, because illegal moves were present as threats.

2) Two to three moves that can't be played is already a lot!

luigi wrote:OK, all the better then. Passive ko is much less restrictive than Tibetan ko

??? how do you know this? it seems like apples and oranges to me, but even so I can't help but feeling that yours is more restrictive.

Tibetan ko turns lots of standard l&d into ko (bulky eye spaces and so on). Luigi ko hugely changes situation where multiple strings of stones are in Atari, and turns a lot of them into ko. Both very broad, but different.

Cycles are a fly on the window. The ko rule is a fly swatted. Anything more drastic is a brick.

hyperpape wrote:1) If there are two to three moves ruled out by this, then there will be several times as many places where the best play is different, because illegal moves were present as threats.

2) Two to three moves that can't be played is already a lot!

1) Yes. Of course, this rule changes the game much more than superko rules, for instance.

2) It doesn't seem that much to me considering that those two or three moves are likely to be ko threats. (And three could be an overestimation anyway. Not every game features a complicated ko fight or lasts more than 300 moves.)

speedchase wrote:

luigi wrote:OK, all the better then. Passive ko is much less restrictive than Tibetan ko

??? how do you know this? it seems like apples and oranges to me, but even so I can't help but feeling that yours is more restrictive.

You're right that they're different things and comparing them is difficult. My reasoning was as follows:

Both rules have in common that they forbid making a capture by playing where your opponent just took one of your stones, and differ in the rest of forbidden plays after an enemy capture. Under Tibetan ko, those forbidden plays imply fundamental changes in life and death but leave the rest of the game mostly intact, while passive ko implies subtle changes in several areas of the game (most of them related to ko fights) but leaves the majority of basic life and death shapes intact.

My impression is that the latter feels closer to Go because I think the balance between life and death is what most strongly defines the character of the game, and it would seem that Tibetan ko tips that balance a bit too much towards life, whilst the diffuse changes introduced by passive ko don't alter that balance one way or the other in any easily identifiable manner.

Most notably, reducing the number of available ko threats can't do it because it also hinders the other player's efforts to kill, and since that's by far the most changed aspect of the game, the opportunities to tip that balance are greatly reduced.

Maybe it all boils down to a question of strategy versus tactics. Making it easier to live requires different long term planning and changes your global picture of the game, whereas making ko fights behave differently and increasing the incentive to capture affect your tactical priorities in the current local battles.

Of course, this is all arguable and you have much more experience with the game anyway, so your impressions may be more accurate.

While life and death may be relatively unchanged under passive ko, it could greatly affect exchanges and many joseki, as suddenly you can't trade, say, a ponnuki in one area for one in another without making a ko threat, and the capture of a dead group or stone could completely change the outcome of a semeai, as when a capture creates an eye but removes the 2nd to last liberty.

skydyr wrote:While life and death may be relatively unchanged under passive ko, it could greatly affect exchanges and many joseki, as suddenly you can't trade, say, a ponnuki in one area for one in another without making a ko threat, and the capture of a dead group or stone could completely change the outcome of a semeai, as when a capture creates an eye but removes the 2nd to last liberty.

More damning, any ko threat involving capture would become false if the ko could be resolved through capture.

Play it out on L19x19 and see what happens. One game with Passive ko, one with Tibetan ko

skydyr wrote:While life and death may be relatively unchanged under passive ko, it could greatly affect exchanges and many joseki, as suddenly you can't trade, say, a ponnuki in one area for one in another without making a ko threat

On the bright side, since ko fights are said by many people to be one of the most interesting aspects of the game, turning simple (but actually infrequent) exchanges into pseudo-ko fights could even be a good thing in some sense. They wouldn't be more or less obvious local replies anymore, but their assessment would depend on the whole board situation.

luigi wrote:

hyperpape wrote:Perhaps even bigger than snapbacks is that a great many trades become impossible.

That's indeed an important difference, but I think such trades are actually much less frequent than one might expect.

In fact, I've reviewed a fair bunch of pro games from my small database of 5000 games (included with the SmartGo demo version) in search of moves that would have been illegal with the passive ko rule (from now on divergent moves)

I don't think your analysis is going to be correct here, because you ignore the possibility that players would strategically set up these positions. A simple endgame example:

Click Here To Show Diagram Code

[go]$$B Black gets a and b
$$ ---------------------
$$ | . . . X b X X X O
$$ | X X X X O O O O O
$$ | O X O O O . . . .
$$ | a X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .[/go]

Assuming the rest of the board is settled B can take 1 and 3.

Or we can make it an L&D problem:

Click Here To Show Diagram Code

[go]$$W W to kill
$$ -----------
$$ | . . O X O
$$ | X X X X O
$$ | . X O O O
$$ | . X O . .
$$ | X O O . .
$$ | O . . . .
$$ | . . . . .[/go]

Mef wrote:

luigi wrote:

hyperpape wrote:Perhaps even bigger than snapbacks is that a great many trades become impossible.

That's indeed an important difference, but I think such trades are actually much less frequent than one might expect.

In fact, I've reviewed a fair bunch of pro games from my small database of 5000 games (included with the SmartGo demo version) in search of moves that would have been illegal with the passive ko rule (from now on divergent moves)

I don't think your analysis is going to be correct here, because you ignore the possibility that players would strategically set up these positions. A simple endgame example:

$$B Black gets a and b
$$ ---------------------
$$ | . . . X b X X X O
$$ | X X X X O O O O O
$$ | O X O O O . . . .
$$ | a X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .

Click Here To Show Diagram Code

[go]$$B Black gets a and b
$$ ---------------------
$$ | . . . X b X X X O
$$ | X X X X O O O O O
$$ | O X O O O . . . .
$$ | a X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .[/go]

Assuming the rest of the board is settled B can take 1 and 3.

Or we can make it an L&D problem:

$$W W to kill
$$ -----------
$$ | . . O X O
$$ | X X X X O
$$ | . X O O O
$$ | . X O . .
$$ | X O O . .
$$ | O . . . .
$$ | . . . . .

Click Here To Show Diagram Code

[go]$$W W to kill
$$ -----------
$$ | . . O X O
$$ | X X X X O
$$ | . X O O O
$$ | . X O . .
$$ | X O O . .
$$ | O . . . .
$$ | . . . . .[/go]

That's true. Making capturing trades impossible makes sente more valuable, which is perhaps the main strategic difference.

BTW, another interesting feature of this rule is that the mirror Go strategy is much harder to sustain.

As a curiosity, either of the following similar rules would make cycles mathematically impossible:

If your opponent has captured n stones on his turn, you can't make a capture on your next n turns. (EDIT: Further stones captured by the opponent are added to n.)

If your opponent has captured n stones on his turn, neither player can make a capture until the total number of non-capturing moves played afterwards equals n.

These rules would change the game completely, but they could be interesting experiments anyway. I suspect the first one would give far too much of an incentive to make captures, but the second one should be more balanced.

If your opponent has captured n stones on his turn, neither player can make a capture until the total number of non-capturing moves played afterwards equals n.

Those last rules would have an interesting feature in that it is capture-sente (for lack of a better term) to capture odd numbers of stones, and capture-gote to capture even numbers.