Fixed Ko Rule: Continued Discussion

HermanHiddema · Post by **HermanHiddema** » Tue Jan 04, 2011 1:26 pm

emeraldemon wrote:
HermanHiddema wrote:You said that superko is easy to understand, then Robert replied that superko is indeed easy to understand, therefore you felt the need to elaborate on why superko is easy to understand?

Yes

Actually as I understand it we're talking about a subtle difference: We both agree that the rules of superko are easy, but Robert said that in his variants the strategy is easy to understand, implying that the strategy of superko is difficult or convoluted. I think the strategy of superko is not significantly more difficult than the strategy of regular ko.

Of course, regular kos are certainly enough to make my head spin

Ah yes, I see your point

I think superko strategy is (far) more difficult than basic ko strategy.

E.g:

Click Here To Show Diagram Code: [go]$$W top side of 19x19 diagram $$ ----------------------------------------- $$ - X X X X X X X X X X X X X X X X X X X - $$ - X . X . X . X . X . X . X . X . X O X - $$ - O X O X O X O X O X O X O X O X O . O - $$ - O O O O O O O O O O O O O O O O O O O - $$ - X X X X X X X X X X X X X X X X X X X -[/go]

Bottom black stones alive. White to play. No ko threats or legal moves anywhere else. Who wins this fight with positional superko? How is the result affected if there are legal moves elsewhere? How is it affected by various numbers of ko threats for either player?

The point, of course, is that superko covers all cycles, no matter how long, and arguing that a situation with three kos is easy does not imply superko is easy for all cycles.

RobertJasiek · Post by **RobertJasiek** » Tue Jan 04, 2011 2:05 pm

Indeed. Various (mostly extremely rare) positions were studied for that superko strategy is extremely difficult (requires hours to years of study or research).

hyperpape · Post by **hyperpape** » Tue Jan 04, 2011 3:04 pm

This is just curiousity, I know it won't sway your interest in these positions, but has such a very difficult case arisen in play? I don't mean Herman's sort of artificial example, but any long-cycle? More than a triple-ko, I guess?

willemien · Post by **willemien** » Tue Jan 04, 2011 3:10 pm

RobertJasiek wrote:Rules application is possible by anybody who understands the rules; therefore also you can write a superko commentary:)

RobertJasiek wrote:Indeed. Various (mostly extremely rare) positions were studied for that superko strategy is extremely difficult (requires hours to years of study or research).

Am I the only one who sees an inconsisency? :rambo:

RobertJasiek · Post by **RobertJasiek** » Tue Jan 04, 2011 3:15 pm

willemien, writing a superko strategy guide does not require to explain all known example shape classes!

hyperpape, I am not sure what has occurred under superko but likely candidates are quintuple kos or several basic kos on the board worth fighting together in some way.

Magicwand · Post by **Magicwand** » Tue Jan 04, 2011 3:18 pm

hyperpape wrote:This is just curiousity, I know it won't sway your interest in these positions, but has such a very difficult case arisen in play? I don't mean Herman's sort of artificial example, but any long-cycle? More than a triple-ko, I guess?

i have seen quadriple ko few times.
even triple ko is hard to apply superko rule.
imagine 4 or 5.

super ko will solve one probem but also will bring many more problems.
i do not understand why people try to rid of no decision rule.
it rarely happens and playing another game should be easy solution.

HermanHiddema · Post by **HermanHiddema** » Tue Jan 04, 2011 3:29 pm

hyperpape wrote:This is just curiousity, I know it won't sway your interest in these positions, but has such a very difficult case arisen in play? I don't mean Herman's sort of artificial example, but any long-cycle? More than a triple-ko, I guess?

Quadruple ko is certainly not unheard of (link gives several examples of them happening in actual play). John Fairbairn mentions at the Triple Ko page that GoGoD has 10 quadruple ko examples and mentions having heard of a quintuple ko in a Japanese amateur game.

Other strange cycles that arose in play include: Sending Three Returning Two (in one of my own games) and Molasses Ko (in a game of T Mark Hall).

hyperpape · Post by **hyperpape** » Tue Jan 04, 2011 6:06 pm

Thanks, all.

RobertJasiek · Post by **RobertJasiek** » Wed Jan 05, 2011 1:33 am

Magicwand wrote:even triple ko is hard to apply superko rule.

Ordinary triple ko is easy to apply under superko. Well, if you have not through about it yet, do so and you will understand the why.

super ko will solve one probem

Like every ko ruleset, superko solves the problem of meaningless endlessly recurring cycles. This is much more than your understatement of [only] "one problem" suggests.

but also will bring many more problems.

Difficult strategy you call problems? If so, yes.

i do not understand why people try to rid of no decision rule.

Because it is an extremely bad rule with gaps and ambiguity:
http://home.snafu.de/jasiek/mistakes.html
http://home.snafu.de/jasiek/j1989c.html
Read the relevant parts of those pages incl. the commentary on rule §12 and don't miss the Interpretative Text! If one spells out No Result Rules properly, then their text becomes more difficult than the other mentioned ko rulesets.

it rarely happens

If rarity is your concern, then you should have nothing against superko! Any strategic difficulties are just (very) rare. So why care?

and playing another game should be easy solution.

One cannot say so in general because of limited tournament schedules. A more generally working solution would be to say that Black (alternatively: White) wins in case of a long cycle.

HermanHiddema · Post by **HermanHiddema** » Wed Jan 05, 2011 3:48 am

Another solution to long cycles: Declare all cycle intersections off limits.
Remove any stones from them and prohibit both players from playing there.

This would apply to all cycles longer than 2 (or longer than 3, if you prefer).

Examples:

Click Here To Show Diagram Code: [go]$$B Triple ko: Before $$ --------------- $$ . X O . O X O . $$ . X O O X X O . $$ . X O . O X O . $$ . X O O X X O . $$ . X O X . X O . $$ . X O O X X O . $$ . X X X O O O . $$ . . . . . . . .[/go]

If the players play through the cycle (6 moves), then:

Click Here To Show Diagram Code: [go]$$B Triple ko: After $$ --------------- $$ . X O C C X O . $$ . X O O X X O . $$ . X O C C X O . $$ . X O O X X O . $$ . X O C C X O . $$ . X O O X X O . $$ . X X X O O O . $$ . . . . . . . .[/go]

All the

marker intersections are now cleared and prohibited. Effectively, the result is seki.

Second example. Eternal life:

Click Here To Show Diagram Code: [go]$$B Eternal life: Before $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X O O O X X O O . . $$ | . O . X . O X . . . $$ --------------------[/go]

If the player play through the (four move) cycle, then:

Click Here To Show Diagram Code: [go]$$B Eternal life: After $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X O O O X X O O . . $$ | . O C C C C X a . . $$ --------------------[/go]

Again, the :ec:

marked points are cleared and prohibited. Again the result is effectively seki.

(Note that in this case, optimal strategy for White would normally be to play at a on move 4, rather than throwing in, because the result is also seki, but with White getting sente and a move on the outside.)

With this rule, the result of long cycles will simply be seki. The players can continue with the game and get a result through play, which is IMO a much preferred solution to any declared result (such as "no result", "draw" or "white/black wins").

You could, of course, still make a distinction between balanced (same number of captures) and unbalanced (different number of captures) cycles, like long cycle rules do, and declare a winner in the unbalanced cases.

RobertJasiek · Post by **RobertJasiek** » Wed Jan 05, 2011 4:16 am

Removing stones with liberties defies the simple beauty of the capture rule. To work out Robert Pauli's / your proposal a bit differently, I suggest to leave the stones on the board but to prohibit playing on any earlier played cycle set intersection. Let me call this the Cycle Set Prohibition Rule.

HermanHiddema · Post by **HermanHiddema** » Wed Jan 05, 2011 4:49 am

RobertJasiek wrote:Removing stones with liberties defies the simple beauty of the capture rule. To work out Robert Pauli's / your proposal a bit differently, I suggest to leave the stones on the board but to prohibit playing on any earlier played cycle set intersection. Let me call this the Cycle Set Prohibition Rule.

This has very different consequences. The rule I suggested effectively results in seki. With this rule, there can be a "winner" of the cycle, with somewhat strange prohibited points remaining.

E.g:

Click Here To Show Diagram Code: [go]$$W Eternal life: Before $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X O O O X X O O . . $$ | . O X X . O X . . . $$ --------------------[/go]

Click Here To Show Diagram Code: [go]$$W First two moves $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X O O O X X O O . . $$ | . O . 2 1 O X . . . $$ --------------------[/go]

Click Here To Show Diagram Code: [go]$$W Next two moves $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X O O O X X O O . . $$ | b O 4 X a 3 X c . . $$ --------------------[/go]

Now, the players are prohibited from playing at a, but Black can capture at b, and White at c resulting in:

Click Here To Show Diagram Code: [go]$$W Eternal life: After $$ | . . . . . . . . . . $$ | . . . . . . . . . . $$ | O O O O O O . . . . $$ | X X X X X O . . . . $$ | X . . . X X O O . . $$ | X . X X a O . O . . $$ --------------------[/go]

This position, where a is prohibited to both players.

Effectively, white has lost the eternal life fight here.

Click Here To Show Diagram Code: [go]$$B $$ --------------------------------------- $$ | . O X . X O . . . . . . . O X a X X O | $$ | O O O X X O . . . . . . . O X X X O . | $$ | . O X X X O . . . . . . . O O X O O O | $$ | O X X . X O . . . . . . . . O O X O . | $$ | X X X X X O . . . . . . . O . O X O O | $$ | O O O O O O . . . . . . . . . X X X X | $$ | . . . . . . . . . . . . . . . . . . . |[/go]

In a similar way, a triple ko consisting of double ko seki and a another ko may in this may result in a favorable result for one player, where the double ko becomes prohibited while one player wins the other ko.

In the above position, if the ko is taken, then the double ko exchanged, then the ko taken back, then the double ko exchanged again, white will "win" the ko, because he is allowed to take at a later. The empty 2-1 point will be prohibited.

Harleqin · Post by **Harleqin** » Wed Jan 05, 2011 7:01 am

I do not think that arbitrary rule amendments can give a satisfactory solution. I believe that a practical ruleset should have a single ko rule that covers all corner cases.

"Positional superko", "situational superko", "natural situational superko", and "double fixed ko"(*) seem to fulfill this requirement. "Basic ko + long cycle tie", "basic ko + fixed ko" do not, while "Basic ko + mushoubu" is a question of perspective.

(*) This has not yet been studied much. It says (roughly) that a move, characterized only by the (unordered) set of its before- and after-position, may not be repeated. I believe it was proposed in some thread either here or on the old godiscussions.com forum.

HermanHiddema · Post by **HermanHiddema** » Wed Jan 05, 2011 7:52 am

Harleqin wrote:I do not think that arbitrary rule amendments can give a satisfactory solution. I believe that a practical ruleset should have a single ko rule that covers all corner cases.

What is wrong with having a set of rules, rather than a single rule, if the set covers all corner cases?

I do think it is bad to have a single rule that does not cover all cases, and to then add rulings on a case by case basis. But I see nothing wrong with rules that treat basic ko different from other cycles, as long as they cover all cases.

RobertJasiek · Post by **RobertJasiek** » Wed Jan 05, 2011 8:12 am

"wrong" would be too strong a word but "disadvantage" fits:

More than one rule makes reading the text, understanding the text as such and thus learning the rules as a newbie / journalist / other interested non-player a bit more difficult. Possibly good layout for a complete single page rules flyer is made harder.

Life In 19x19

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