What's the logic behind natural situational superko?

[willemien]

On sensei's library QuickQuestions there was a question on NaturalSituationalSuperko


http://senseis.xmp.net/?topic=2359

I don't know the exact answer so i just put it here.

i made a preliminary responce:

To be honnest I don't know.

My guess would be it is to allow as much as possible. (so that the superko rule prevents as little as possible.

you can see the progression

1. positional superko prevents the most
2. situational superko allows more
3. natural situational superko allows a bit more
4. ...
5. Repeat of moves (in the same position the same player may not make the same move) allows even more.

I think Repeat of moves is the most allowing superko rule that is possible while it still will make sure a game will always come to an end. (but it can take much longer)

There is a discussion if it all makes even can make a theoretical difference.

But maybe ghere people can tell more.

[tundra]

Well, this is also only a guess:

AFAIK, none of the various superko rules ever prevent a player from passing. They only place restrictions on moves in which a stone is placed on the board. (In a way, this is not surprising - otherwise, we would need a special rule to allow the two consecutive passes that end the game...)

So, the feeling may be that passes should not count in considering board repetitions. That is, if Black created an earlier position by passing, then he should be free to re-create it later on by playing a stone. (He cannot play such a stone a second time, of course, since then superko is violated.)

Or to view it another way: All the superko rules allow this order of plays: Black first creates a position by playing a stone, then re-creates it by passing. But natural situational superko also allows the other order: Black first creates a position by passing, then re-creates it by playing a stone.

It does have a certain logic to it, though I am not sure how easy it would be to administer such a rule.

But as I said, this is just a guess. Perhaps Robert Jasiek or Bill Spight would be better people to ask.

[Mr. Mormon]

All the superko rules allow this order of plays: Black first creates a position by playing a stone, then re-creates it by passing. But natural situational superko also allows the other order: Black first creates a position by passing, then re-creates it by playing a stone.

Now I understand NSSK. Thank you.

However, although this rule allows more moves than SSK, I find the complication of passing annoying, and not just in ko. Who needs passing if suicide's allowed, and who needs two passes when resigning is allowed? If the option of passing did not exist, perhaps a ko rule could be agreed on for once in 3,000 years...

[palapiku]

Who needs passing if suicide's allowed

Surely a superko rule that forbids passing would also forbid the suicide of one stone? They have the same effect on the board.

[palapiku]

In fact, imagine a board that's fully filled with living groups with one-space eyes. With natural situational superko and with suicide allowed, the players may play into each of the opponent's eyes once, not changing the board, after which they run out of "passes".

To me this is ridiculous enough to be a good argument against both natural situational superko and against suicide.

[RobertJasiek]

Firstly there are different basic classes of superko-like rules:

1) considering only the position

2) considering the sitation

3) related to ending by 3 passes (Robinson-Olmsted style)

4) related to evaluation (Spight style)

5) maximizing low-level variation (fixed-ko-rule)

Secondly the purpose of my invention of the Natural Sitational Superko Rule was to suggest the best rule of class (2), i.e. after assuming to have already decided on class (2). (This does not say anything at all though which class should be chosen for which purposes. So it is not at all any decision about choosing the best class and the possibly overall best superko rule(s).)

Note that Terry Benson, major author of AGA 1991 Rules, later claimed to have intended Natural Sitational Superko. If so, we would have been inventing the rule independently of each other. (Everybody else incl. me interprets the AGA 1991 ko rule as Sitational Superko.)

For class (2), there are two (major) rules: a) the Sitational Superko Rule, b) the Natural Sitational Superko Rule.

The reason for inventing (b) and calling it better than (a) is: Under (b), the causes and consequences for bans are the same: plays. Under (a), the causes (plays or passes) for bans differ from the consequences (plays only) for bans; this is inconsistent. Consistent rules are better than inconsistent rules, so (b) is the better of the two choices.

[Mr. Mormon]

Surely a superko rule that forbids passing would also forbid the suicide of one stone? They have the same effect on the board.

Not with situational superko. Of course, two consecutive 'passes' would not be allowed, but someone would have resigned by then.

In fact, imagine a board that's fully filled with living groups with one-space eyes. With natural situational superko and with suicide allowed, the players may play into each of the opponent's eyes once, not changing the board, after which they run out of "passes".

Actually, what would happen there is that (say) black would continually 'pass' while white would have to play inside her eyes until captured. Isn't this also a problem in any ruleset when two passes end the game?

[Mr. Mormon]

Nevermind. Since white is ahead, she would want to end the game. Go does need passing after all.

[Mr. Mormon]

For class (2), there are two (major) rules: a) the Sitational Superko Rule, b) the Natural Sitational Superko Rule.

The reason for inventing (b) and calling it better than (a) is: Under (b), the causes and consequences for bans are the same: plays. Under (a), the causes (plays or passes) for bans differ from the consequences (plays only) for bans; this is inconsistent. Consistent rules are better than inconsistent rules, so (b) is the better of the two choices.

(a) is consistent if "passing is always allowed" doesn't override superko, as I (incorrectly?) assumed two posts up.

[RobertJasiek]

How does that make (a) consistent?

[Mr. Mormon]

causes (plays or passes) for bans differ from the consequences (plays only)

Instead of making SSK consistent by removing passes from causes, add passes to consequences. If passing would result in a repeated situation, one may not pass.

[Harleqin]

I am pretty sure that having no Zugzwang is essential for Go. Passing must always be allowed.

[Mr. Mormon]

Why?

[palapiku]

Why?

Because there's no group tax anymore

[Mr. Mormon]

I don't understand. What does group tax have to do with forced bad plays?