The "no ban in double ko" rule to solve pass-for-ko issue ?

Gérard TAILLE · #1

The ambituous here is to solved ONLY the pass-for-ko issue (the intention is not to clarify points like "enable" interpretation).

The traditionnal interpretation of J89 is a pass-for-ko for each ko and we know that this strict interpretation does not work with double ko.
We all know that at least two possibilities exist to solve this problem:
1) Jann interpretation of the rule => pass-for-ko once
2) J2003 rule => ko-pass
In both cases the main problem is solved because the double ko is finally handled like in normal play.
Unfortunately side effects appear with both solutions simply because the double ko situations (for which normal play should be used) are not clearly identified.
My proposal is to use the "pass-for-ko for each ko" but to add a definition for double ko situations in which normal play is used instead.

Confirmation phase:
Use of strict pass-for-ko for each ko with the adding "no ban in double ko" rule

Definitions:
Two ko are said to be a "strong double ko" if these two ko are adjacent to both a white group and a black group.
Two ko are said to be a "weak double ko" if these two ko are adjacent to the same group of stones and if this group of stones has no "strong double ko"
A "critical double ko situation" is a "strong double ko" or a "weak double ko" in which the two ko are taken by the same player

Rule:
"No ban in double ko" rule: in a "critical double ko situation" pass-for-ko requests can be ignored

Example 1:

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

Click Here To Show Diagram Code: [go]$$B $$ ------------------------------- $$ | O . O . X X 2 . O . . O X . . $$ | O O O X O X X O O O O O X . . $$ | X X X O 1 O O O X X X X X . . $$ | . . X O O O X X X . . . . . . $$ | . . X X X X X . . . . . . . . $$ | . . . . . . . . . . . . . . . $$ | . . . . . . . . . . . . . . .[/go]

Click Here To Show Diagram Code: [go]$$B $$ ------------------------------- $$ | O . O . B B Q T W . . W X . . $$ | O O O X T B B W W W W W X . . $$ | X X X W Y W W W X X X X X . . $$ | . . X W W W X X X . . . . . . $$ | . . X X X X X . . . . . . . . $$ | . . . . . . . . . . . . . . . $$ | . . . . . . . . . . . . . . .[/go]

The two marked ko are a strong double ko

Click Here To Show Diagram Code: [go]$$B pass $$ ------------------------------- $$ | O . O 6 X X . 3 O . . O X . . $$ | O O O X 4 X X O O O O O X . . $$ | X X X O X O O O X X X X X . . $$ | . . X O O O X X X . . . . . . $$ | . . X X X X X . . . . . . . . $$ | . . . . . . . . . . . . . . . $$ | . . . . . . . . . . . . . . .[/go]

is allowed due to the "no ban in double ko" rule

Example 2:

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

Click Here To Show Diagram Code: [go]$$B $$ ----------------- $$ | O X . X . O . | $$ | 1 O X X X O O | $$ | O 2 O O X X O | $$ | O O O . O X O | $$ | X X O O X X O | $$ | . X X O O O . | $$ | X . X X X O O | $$ -----------------[/go]

Click Here To Show Diagram Code: [go]$$B $$ ----------------- $$ | T X . X . O . | $$ | Y W X X X O O | $$ | W W W W X X O | $$ | W W W T Q X O | $$ | X X W W X X O | $$ | . X X W W W . | $$ | X . X X X W W | $$ -----------------[/go]

The two marked ko are a weak double ko

Click Here To Show Diagram Code: [go]$$B pass pass $$ ----------------- $$ | 4 8 6 X . O . | $$ | X O X X X O O | $$ | O O O O X X O | $$ | O O O 3 O X O | $$ | X X O O X X O | $$ | . X X O O O . | $$ | X . X X X O O | $$ -----------------[/go]

is allowed due to the "no ban in double ko" rule

Example 3:

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

Click Here To Show Diagram Code: [go]$$B $$ +---------------------–---------- $$ | . X X O X O . . . O B Q T W . | $$ | X O . O X O . . . O B B W W W | $$ | O O X X X O . . . O B . B W Y | $$ | O X X O O O . . . O B B B B T | $$ | . O X O . . . . . O O O O B B | $$ | . O X O . . . . . . . . O O O | $$ | O X X O . . . . . . . . . . . | $$ | O O O O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . |[/go]

The two marked ko are a strong double ko

Click Here To Show Diagram Code: [go]$$B pass-for-ko at $$ +---------------------–---------- $$ | 2 X X O X O . . . O X O 7 O . | $$ | 5 O 1 O X O . . . O X X O O O | $$ | O O X X X O . . . O X . X O X | $$ | O X X O O O . . . O X X X X 8 | $$ | 6 O X O . . . . . O O O O X X | $$ | 4 O X O . . . . . . . . O O O | $$ | O X X O . . . . . . . . . . . | $$ | O O O O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . |[/go]

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

pass -for-ko on the right
:w10:

pass for ko on the LEFT

Click Here To Show Diagram Code: [go]$$Bm11 pass-for-ko on the right $$ +---------------------–---------- $$ | 4 X X . X O . . . O X 2 X O . | $$ | X O X . X O . . . O X X O O O | $$ | O O X X X O . . . O X . X O 1 | $$ | O X X O O O . . . O X X X X O | $$ | O O X O . . . . . O O O O X X | $$ | O O X O . . . . . . . . O O O | $$ | O X X O . . . . . . . . . . . | $$ | O O O O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . |[/go]

is allowed due to the "no ban in double ko" rule

Click Here To Show Diagram Code: [go]$$Bm11 pass-for-ko on the right $$ +---------------------–---------- $$ | O X X . X O . . . O X O 5 O . | $$ | M O X . X O . . . O X X O O O | $$ | O O X X X O . . . O X . X O X | $$ | O X X O O O . . . O X X X X 6 | $$ | O O X O . . . . . O O O O X X | $$ | O O X O . . . . . . . . O O O | $$ | O X X O . . . . . . . . . . . | $$ | O O O O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . |[/go]

is allowed due to the "no ban in double ko" rule

Click Here To Show Diagram Code: [go]$$Bm11 $$ +---------------------–---------- $$ | O X X . X O . . . O X 0 X O . | $$ | 8 O X . X O . . . O X X O O O | $$ | O O X X X O . . . O X . X O 9 | $$ | O X X O O O . . . O X X X X O | $$ | O O X O . . . . . O O O O X X | $$ | O O X O . . . . . . . . O O O | $$ | O X X O . . . . . . . . . . . | $$ | O O O O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . |[/go]

is allowed due to the "no ban in double ko" rule

and black has not been able to prove that the two white stones captured at the very beginning of the sequence are dead!

Example 4:

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

Click Here To Show Diagram Code: [go]$$B $$ ----------------- $$ | X O O . . . . . $$ | . B O O O . . . $$ | B B B B O . . . $$ | T B Q B O . . . $$ | Y W T W X . . . $$ | W W W W X . . . $$ | . W X X X . . . $$ | W W X . . . . . $$ | X X X . . . . . $$ | . . . . . . . . $$ | . . . . . . . .[/go]

The two marked ko are a strong double ko

Click Here To Show Diagram Code: [go]$$W $$ ----------------- $$ | X O O . . . . . $$ | 1 X O O O . . . $$ | X X X X O . . . $$ | 3 X O X O . . . $$ | X O 2 O X . . . $$ | O O O O X . . . $$ | . O X X X . . . $$ | O O X . . . . . $$ | X X X . . . . . $$ | . . . . . . . . $$ | . . . . . . . .[/go]

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

Black cannot retake the ko in the corner by requesting the application of the "no ban in double ko" rule because the black group has already a strong double ko => the ko in the corner cannot be part of a weak double ko

jann · #2

First, if the official J89 rule really only forbids recapture in kos the player have not yet passed for, then there is no problem and no issue to fix.

Second, you cannot invent new and complicated rules with this ease. Many players, even Japanese players, are not even aware of the pass-for-ko rule. And rules that refer to specific shapes seem like 50+ years step back in the past, the age of precedents.

Rules need to be logical, not just in the sense of clear definitions, but also in the sense that they must have a good answer (beyond the desired effect in certain shapes) to the question: WHY?

Gérard TAILLE · #3

jann wrote:

First, if the official J89 rule really only forbid recapture in kos the player have not yet passed for, then there is no problem and no issue to fix.

Second, you cannot invent new and complicated rules with this ease. Many players, even Japanese players, are not even aware of the pass-for-ko rule. And rules that refer to specific shapes seem like 50+ years step back in the past, the age of precedents.

Rules need to be logical, not just in the sense of clear definitions, but also in the sense that they must have a good answer (beyond the desired effect in certain shapes) to the question: WHY?

The idea cannot be to invent a new rule. On contrary the idea is to have a better understanding of what is behind japonese rule.

I agree with you that the different point of the rule must have sense and must be justified.

Maybe I am wrong but in J89 one basic idea is to create some independancy between ko and their ko theats. The pass-for-ko defined in J89 is here to create this independancy but the pass-for-ko is not a naturel tool itself in go world; it is in J89 only to try to reach this independancy. It is fine but it does not work properly with double ko. Why? One of the reasons is that in double ko situations the two ko cannot be handled independantly. On contrary in double ko situation the two ko are strondly linked and that is the reason why pass-for-ko cannot work in double ko situation and that is the reason why simply normal play should be used in double ko.

You may find complicated to introduce the double ko item but in my mind a double ko situation is very easily recognized by any go player and this double ko situation is not really linked to specific shapes and can appear in various positions.

As soon as we recognize that a double ko work differently than a simple ko we must be careful when defining how to handle ko in confirmation phase. My analyse is that pass-for-ko is fine for simple ko but normal play is far better for double ko.

Cassandra · #4

Gérard TAILLE wrote:

Maybe I am wrong but in J89 one basic idea is to create some independancy between ko and their ko theats. The pass-for-ko defined in J89 is here to create this independancy but the pass-for-ko is not a naturel tool itself in go world; it is in J89 only to try to reach this independancy. It is fine but it does not work properly with double ko. Why? One of the reasons is that in double ko situations the two ko cannot be handled independantly. On contrary in double ko situation the two ko are strondly linked and that is the reason why pass-for-ko cannot work in double ko situation and that is the reason why simply normal play should be used in double ko.

The idea is NOT to "create some independancy between ko and their ko threats".

The first idea is to make the L&D assessment independent of KO-THREATS. The best way to become independent of something is to inhibit that something. Allowing the player who captured into a SINGLE ko-shape to play a second move in a row locally (the ko-capture being the first one) serves that purpose.
=> There are simply NO ko-threats during L&D status confirmation that would make the re-capture into a ko-shape possible.
=> If a player considers it unbearable to have the opponent playing this kind of two moves in a row during status confirmation, they should have played a teire during play. This also makes "open" ko-shapes filled.

The second idea is to make the L&D assessment independent of KO-FIGHTS. The best was to become independent of something is to inhibit that something. J89 chose the method to make ko-fights an OPTIONAL issue, in the sense that BOTH players must be fine with it if BOTH have at least one ko-shape each to re-capture into.
=> There are simply NO RE-captures into ko-shapes, as long as not ALL ko-bans have been lifted.
=> Double-ko have lost their virtue.

It follows Japanese understanding that "ko" shall NOT play the slightest role for the judgement on L&D. It does not make any sense at all to doubt this understanding by fighting its consequences. Just play a non-Japanese variant of the game, instead.

gennan · #5

I suppose the literal Japanese rules are not clearly stated, but my understanding has always been that their intention is that there are no ko threats in hypothetical play (everything else is the same as normal play). And this is per situation where there is a dispute.

kvasir · #6

gennan wrote:

I suppose the literal Japanese rules are not clearly stated, but my understanding has always been that their intention is that there are no ko threats in hypothetical play (everything else is the same as normal play). And this is per situation where there is a dispute.

The intention with the pass-ko seems to be (in status confirmation only)
:w1:

Not allow fighting a ko using ko threats
:w2:

Allow the color with less ko threats to capture back in a ko when the other color refuses to finish the ko

It is :w2:

that causes difficulties, aside from wild variations during status confirmation, there is a problem that it is often possible to force a cycle in double-ko like shapes. In normal play you can't cycle in a double ko but using the pass-ko rule you can by passing for the ko force the other side to either allow two moves in a row in the ko or also pass for the ko.

I think it is this double-ko cycle that Gerard is trying to rule out. It is really not clear how to handle such arguments by referring to the rules (because they seem to result in incorrect results), it is also tricky because when you ban the cycle you are also taking sides because one or the other side would effectively be forbidden from continuing the cycle.

Gérard TAILLE · #7

A agree with Gennan and Kvasir, the intention for me is certainly that ko fight have not to take place in confirmation phase.

The point I discovered is that it exist two types of ko: the "fighting" ko for which a ko fight make sense and the "no fighting" ko for which ko fight simply does not make sense.

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

In this basic double ko situation there are no ko fight. If one player takes one ko the opponent takes the other ko and nothing has changed. The two ko are miai and nothing can happen => no ko fight exist here.

Let's take now the following example:

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

Do you see ko threats? Do you see ko fight?
In the position above white is dead in any area scoring rule and white is dead in NORMAL play in any territory rule, even if it is white to play first.
What is the intention for handling these ko in a confirmation phase?

RobertJasiek · #8

There are more than two major ko types (Fighting Ko vs. Disturbing Ko): http://home.snafu.de/jasiek/ko_types.pdf

Gérard TAILLE · #9

RobertJasiek wrote:

There are more than two major ko types (Fighting Ko vs. Disturbing Ko): http://home.snafu.de/jasiek/ko_types.pdf

OC Robert but here I am only in the context of the confirmation phase and in this context it seems that only two types of ko are to be distinguished. The ko corresponding to what I call a "critical double ko" and the others. Forget about the wording "fighting" ko I used because I see you used also this wording but with another definition.

Cassandra · **#10**

Gérard TAILLE wrote:

What is the intention for handling these ko in a confirmation phase?

Punish Black for his final mistake during "play".

jann · **#11**

Gérard TAILLE wrote:

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

Do you see ko threats? Do you see ko fight?
In the position above white is dead in any area scoring rule and white is dead in NORMAL play in any territory rule, even if it is white to play first.
What is the intention for handling these ko in a confirmation phase?

Some ko threats and some ko play is visible, just - like you say - the result is double ko life in normal play. Since incorrect rulings can be avoided here by simply honoring normal (ko) play, Occam doesn't see a need to introduce any further concepts.

kvasir · **#12**

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

This position demonstrates how dangerous it is to try to pick a winning side in ko fights for the purpose of status confirmation.

One question I have that pertains to this position is how many pass-ko bans do we really need for each player? In this position black is dead because white can create two pass-ko bans in time to fill blacks last two liberties. Is it really needed to allow multiple pass-ko bans on the same player to achieve the desired effect? For example if white had to pick which ko had a pass-ko ban (that is one or the other ko stone would not be subject to a pass-ko), that would solve this position. That is if a player is allowed only one pass-ko ban at a time, could that work? If not, how many pass-ko bans do we really need?

jann · **#13**

kvasir wrote:

That is if a player is allowed only one pass-ko ban at a time, could that work?

I dont' think so, see the positions in the Korean/Japanese topic for reason (left-right ko interaction).

kvasir · **#14**

jann wrote:

kvasir wrote:

That is if a player is allowed only one pass-ko ban at a time, could that work?

I dont' think so, see the positions in the Korean/Japanese topic for reason (left-right ko interaction).

But the result is exactly what you want, no? Black could capture the left side but this allows white to play new stones on the right (because black can't use pass-ko to defend). This is the seki that one would expect because starting two kos surely leads to a trade, not one side winning both kos.

jann · **#15**

Sure, but I meant wouldn't work in the Japanese sense (which implies being able to "fight" several kos in parallel without interaction).

Also, for this behavior you don't need any ko-pass-ban, just normal ko confirmation. And a left-right seki may be more fair than the Japanese result in that particular example, this is still not 100% correct (robs B if extra threat removal is also necessary).

Gérard TAILLE · **#16**

kvasir wrote:

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

This position demonstrates how dangerous it is to try to pick a winning side in ko fights for the purpose of status confirmation.

One question I have that pertains to this position is how many pass-ko bans do we really need for each player? In this position black is dead because white can create two pass-ko bans in time to fill blacks last two liberties. Is it really needed to allow multiple pass-ko bans on the same player to achieve the desired effect? For example if white had to pick which ko had a pass-ko ban (that is one or the other ko stone would not be subject to a pass-ko), that would solve this position. That is if a player is allowed only one pass-ko ban at a time, could that work? If not, how many pass-ko bans do we really need?

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

Could you explain your proposal on the mooshine life position?

kvasir · **#17**

It is exactly the same as example 11 because the normal ko rule prevents white from taking again in the double-ko.

Click Here To Show Diagram Code: [go]$$B pass for $$ --------------------- $$ | . . . X O X 2 X . | $$ | . . . X O O X X X | $$ | . . . X O . O X O | $$ | . . . X O O O O 3 | $$ | . . . X X X X O O | $$ | . . . . . . X X X | $$ | X X X X . . . . . | $$ | O O O X X . . . . | $$ | 5 O 1 O X . . . . | $$ ---------------------[/go]

No one really knows why example 11 has white pass for :b1:

instead of :b3:

and not create the pass-ko cycle in the double-ko. You will need another explanation of this (as you are actually working on) but maybe some of the tricky cases could be handled by limiting the number of pass-ko bans? I did not mean to put this up against some method to treat the double-ko cycle (that some believe doesn't exists for some reason) but to avoid using ko shapes to play multiple approach moves during status confirmation.

Example 7-2 (a bent-4 vs. 10'000 year ko) also works fine because again there is a point when two ko bans are needed buy one is provided with the normal ko rule.

I do not quite see why one needs to allow multiple pass-ko bans to get "Japanese" results. Obviously, there are different results in positions when one side could otherwise use pass-ko to play multiple moves in a row but that is not really bread and butter "Japanese" approach is it? Maybe there is some position someone came up with? But (by potentially fault intuition) I'd suggest that positions that require multiple pass-ko bans are quite in a flux, having more than one possible ko fight at once.

Gérard TAILLE · **#18**

kvasir wrote:

It is exactly the same as example 11 because the normal ko rule prevents white from taking again in the double-ko.

No one really knows why example 11 has white pass for :b1:

instead of :b3:

and not create the pass-ko cycle in the double-ko. You will need another explanation of this (as you are actually working on) but maybe some of the tricky cases could be handled by limiting the number of pass-ko bans? I did not mean to put this up against some method to treat the double-ko cycle (that some believe doesn't exists for some reason) but to avoid using ko shapes to play multiple approach moves during status confirmation.

Example 7-2 (a bent-4 vs. 10'000 year ko) also works fine because again there is a point when two ko bans are needed buy one is provided with the normal ko rule.

I do not quite see why one needs to allow multiple pass-ko bans to get "Japanese" results. Obviously, there are different results in positions when one side could otherwise use pass-ko to play multiple moves in a row but that is not really bread and butter "Japanese" approach is it? Maybe there is some position someone came up with? But (by potentially fault intuition) I'd suggest that positions that require multiple pass-ko bans are quite in a flux, having more than one possible ko fight at once.

Click Here To Show Diagram Code: [go]$$B $$ --------------------- $$ | . . . X O X 2 X . | $$ | . . . X O O X X X | $$ | . . . X O . O X O | $$ | . . . X O O O O 3 | $$ | . . . X X X X O O | $$ | . . . . . . X X X | $$ | X X X X . . . . . | $$ | O O O X X . . . . | $$ | . O 1 O X . . . . | $$ ---------------------[/go]

The position reached is the following:

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

In this position black has created two pass-for-ko ban => is white allowed to retake the ko at the bottom?

Compare with the following position:

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

Click Here To Show Diagram Code: [go]$$W $$ ------------------- $$ | . O X 1 X X O . . $$ | O O O X 2 X O . . $$ | X O O O X O O . . $$ | 3 X O O X X O . . $$ | X X X X . X O . . $$ | X X O X X X O . . $$ | O O O O O O O . . $$ | . . . . . . . . . $$ | . . . . . . . . .[/go]

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

and white has created two pass-for-ko ban => is black allowed to retake the ko at the top?

kvasir · **#19**

Click Here To Show Diagram Code: [go]$$B $$ --------------------- $$ | . . . X O X 2 X . | $$ | . . . X O O X X X | $$ | . . . X O . O X O | $$ | . . . X O O O O 3 | $$ | . . . X X X X O O | $$ | . . . . . . X X X | $$ | X X X X . . . . . | $$ | O O O X X . . . . | $$ | . O 1 O X . . . . | $$ ---------------------[/go]

White is not allowed to take at the bottom because black chooses to protect there with the pass-ko, likewise white is not allowed to take in the double-ko because of the regular ko rule. There is no difference because black only needs to protect one ko using pass-ko (hypothetically because there is the pass-ko double-ko cycle anyway).

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

It would be up to white which ko to protect with pass-ko, but he could not protect both if the number of active pass-ko bans was limited to one per player at time. The position is symmetric so white just picks either one and black then takes the other ko.

Please come up with something to challenge this if I was able to explain what I meant

What I am trying to say is that if each player is allowed to protect one ko at a time using pass-ko it seems to work with all the J89 examples and rule out some forms of pass-ko abuse (for lack of a neutral phrase). It is also similar to pass-once but doesn't preclude using the pass-ko rule repeatedly in the same shape.

Gérard TAILLE · **#20**

kvasir wrote:

Click Here To Show Diagram Code: [go]$$B $$ --------------------- $$ | . . . X O X 2 X . | $$ | . . . X O O X X X | $$ | . . . X O . O X O | $$ | . . . X O O O O 3 | $$ | . . . X X X X O O | $$ | . . . . . . X X X | $$ | X X X X . . . . . | $$ | O O O X X . . . . | $$ | . O 1 O X . . . . | $$ ---------------------[/go]

White is not allowed to take at the bottom because black chooses to protect there with the pass-ko, likewise white is not allowed to take in the double-ko because of the regular ko rule. There is no difference because black only needs to protect one ko using pass-ko (hypothetically because there is the pass-ko double-ko cycle anyway).

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

It would be up to white which ko to protect with pass-ko, but he could not protect both if the number of active pass-ko bans was limited to one per player at time. The position is symmetric so white just picks either one and black then takes the other ko.

I do not understand. As in the previous example white can choose simply to protect the ko at the top and the other ko is protected by regular ko. What is the difference?

The "no ban in double ko" rule to solve pass-for-ko issue ?

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