Kakao janggi has 2 types of repetition rules.

[cjssh1002]

Kakao janggi has 2 types of repetition rules. I explain to you the repetition rule. I hope you apply this rule to the FS-engine(modern).

*A: counter position of Repeat

1. First repetition rule: B-A 1 time, C-A 2 times
2. 3rd repetition rule: B-A 3 times
   • Can be : B-A 2 times, C-A 1 time

No.2 has already been applied. However, No.1 has not yet been applied.

[ianfab]

Thanks. If I understand correctly, A/B/C refer to positions, not moves, so does this mean the repetition detection in Kakao Janggi is based purely on positions, and not on moves? If this is the case, that would simplify matters for me.

Currently, repetition detection in Fairy-Stockfish is purely based on the reoccurrence of a single position, so it does not matter how many other positions occur in between or in which order. Therefore it does not depend on being a straightforward back-and-forth movement pattern with positions repeating like A-B-C-D-A-B-C-D-A or the like.

If this does not cover the scenario you are referring to, can you please explain it in more detail? I am not sure yet whether A/B/C in your patterns above refer to moves, positions, or positions with the same side to move.

[cjssh1002]

Exactly, it is based on the order of positions. Any repetition other than this are not included in the scenario.

[ianfab]

Summary from a discussion on discord on the criteria for prohibiting a repetition in Kakao Janggi:

• The repetition detection is solely based on the moves of one side
• Repetition does not apply to king moves
• A repetition is prohibited in the case a piece moves between two squares A and B two times in a row (ignoring opponent's moves) if the previous move ended on square A (i.e., a move by the same piece): any->A A->B B->A A->B B->A. The last move in this sequence is illegal.

[ianfab]

@cjssh1002 I tried to implement the above rules in https://github.com/ianfab/Fairy-Stockfish/commit/cabb1f562092235e53c3f755a503c903816144c0 and it seems to work, but I did not have much time to test it yet. If you like to test it already, feel free to do so. Feedback would be very welcome. The rule is only applied for the janggimodern variant.

[cjssh1002]

I forgot about the only 1 rules.

• Repetition does not apply to "Wazir" moves.

Even if use "pass" during the repeat, the repeat counter is maintained. (When passing after 2 repetitions) This means that a new counter will not start after the "pass".

[ianfab]

Update:

• The repetition detection is solely based on the moves of one side
• Repetition does not apply to king and guard moves
• Repeated passing does not count as a repetition. Passing moves are skipped when checking for a sequence of repeated moves, so they do not reset the repetition count. (Is this correct?) Passing moves reset the repetition count, except for when the passing move occurs right before the move that is illegal.
• A repetition is prohibited in the case a piece moves between two squares A and B two times in a row (ignoring opponent's moves) if the previous move ended on square A (i.e., a move by the same piece): any->A A->B B->A A->B B->A. The last move in this sequence is illegal.

[cjssh1002]

Yes it is correct.

[ianfab]

I tried to fix the reported issues, please have another look: https://github.com/ianfab/Fairy-Stockfish/commit/bee163eabaeec25ef84c25e0fbc492632e762cc7

[cjssh1002]

You must be tired. Thank you for your effort. ^_^ Now me and my janggi cafe members will fully test for the official master merge.

[cjssh1002]

There is rule that needs to be modified. This is a kakao janggi rule that i was very hard to find.

• Movements that can capture pieces are not included in the repeat counter.
• After capturing the piece, that the piece is reset repeat counter.