Xiongqi

Rule System for Xiongqi (熊棋, “Panda Chess”) built on the Game Protocol.

1. Board

8×8 grid encoded in CELL.

Valid coordinates: a1–h8

FEEN serialization: rank 8 → rank 1, file a → file h, / between ranks.

River: conceptual boundary between ranks 4 and 5.

Side	Before river	After river
First (South)	ranks 1–4	ranks 5–8
Second (North)	ranks 5–8	ranks 1–4

2. Style

SNN	SIN	Side
`Xiongqi`	`X`	first (South)
`Xiongqi`	`x`	second (North)

3. Pieces

All pieces encoded in PIN.

PIN	Name	Notes
`G^`	General	Terminal (initial)
`D^`	Dragon	Terminal (after face-to-face transformation)
`A`	Advisor
`B`	Bear
`C`	Cannon	Screen capture
`E`	Empress	From Soldier promotion
`H`	Horse	Blockable
`R`	Chariot
`S`	Soldier	Before river
`+S`	Soldier	After river
`g^`	General	Terminal (initial)
`d^`	Dragon	Terminal (after face-to-face transformation)
`a`	Advisor
`b`	Bear
`c`	Cannon
`e`	Empress
`h`	Horse
`r`	Chariot
`s`	Soldier	Before river
`+s`	Soldier	After river

4. Initial Position

Encoded in FEEN:

rhbag^bhr/2c2c2/ssssssss/8/8/SSSSSSSS/2C2C2/RHBAG^BHR / X/x

5. Movements

All pseudo-legal moves encoded in GGN. Patterns shown are representative.

5.1 General

{
  "X:G^": {
    "e4": {
      "d4": [{ "must": { "d4": "empty" } }, { "must": { "d4": "enemy" } }],
      "e3": [{ "must": { "e3": "empty" } }, { "must": { "e3": "enemy" } }],
      "e5": [{ "must": { "e5": "empty" } }, { "must": { "e5": "enemy" } }],
      "f4": [{ "must": { "f4": "empty" } }, { "must": { "f4": "enemy" } }]
    }
  }
}

One square orthogonally. No palace restriction.

5.2 Dragon

{
  "X:D^": {
    "e4": {
      "d4": [{ "must": { "d4": "empty" } }],
      "e3": [{ "must": { "e3": "empty" } }],
      "e5": [{ "must": { "e5": "empty" } }],
      "f4": [{ "must": { "f4": "empty" } }],
      "a4": [{ "must": { "b4": "empty", "c4": "empty", "d4": "empty", "a4": "enemy" } }],
      "e1": [{ "must": { "e2": "empty", "e3": "empty", "e1": "enemy" } }]
    }
  }
}

Non-capturing: one square orthogonally.
Capturing: any distance orthogonally (like Chariot). Path must be clear.

5.3 Advisor

{
  "X:A": {
    "e4": {
      "d3": [{ "must": { "d3": "empty" } }, { "must": { "d3": "enemy" } }],
      "d5": [{ "must": { "d5": "empty" } }, { "must": { "d5": "enemy" } }],
      "f3": [{ "must": { "f3": "empty" } }, { "must": { "f3": "enemy" } }],
      "f5": [{ "must": { "f5": "empty" } }, { "must": { "f5": "enemy" } }]
    }
  }
}

One square diagonally. No palace restriction.

5.4 Bear

{
  "X:B": {
    "c1": {
      "f4": [
        { "must": { "d2": "empty", "e3": "empty", "f4": "empty" } },
        { "must": { "d2": "empty", "e3": "empty", "f4": "enemy" } }
      ]
    }
  }
}

Any number of squares diagonally (like Chess Bishop). Path must be clear.

5.5 Cannon

{
  "X:C": {
    "c2": {
      "c5": [{ "must": { "c3": "empty", "c4": "empty", "c5": "empty" } }],
      "c8": [
        { "must": { "c3": "empty", "c4": "empty", "c5": "empty", "c6": "empty", "c8": "enemy" }, "deny": { "c7": "empty" } }
      ]
    }
  }
}

Non-capturing: any distance orthogonally. Path must be clear.
Capturing: jumps exactly one piece (screen), then captures. Path before screen must be clear; path after screen must be clear.

5.6 Empress

{
  "X:E": {
    "d4": {
      "d8": [{ "must": { "d5": "empty", "d6": "empty", "d7": "empty", "d8": "empty" } }, { "must": { "d5": "empty", "d6": "empty", "d7": "empty", "d8": "enemy" } }],
      "c2": [{ "must": { "c2": "empty" } }, { "must": { "c2": "enemy" } }],
      "e2": [{ "must": { "e2": "empty" } }, { "must": { "e2": "enemy" } }],
      "b3": [{ "must": { "b3": "empty" } }, { "must": { "b3": "enemy" } }],
      "f3": [{ "must": { "f3": "empty" } }, { "must": { "f3": "enemy" } }],
      "b5": [{ "must": { "b5": "empty" } }, { "must": { "b5": "enemy" } }],
      "f5": [{ "must": { "f5": "empty" } }, { "must": { "f5": "enemy" } }],
      "c6": [{ "must": { "c6": "empty" } }, { "must": { "c6": "enemy" } }],
      "e6": [{ "must": { "e6": "empty" } }, { "must": { "e6": "enemy" } }]
    }
  }
}

Chariot mode: any distance orthogonally. Path must be clear.
Knight mode: L-shape (all 8 directions). Jumps freely.

5.7 Horse

{
  "X:H": {
    "b1": {
      "a3": [{ "must": { "b2": "empty", "a3": "empty" } }, { "must": { "b2": "empty", "a3": "enemy" } }],
      "c3": [{ "must": { "b2": "empty", "c3": "empty" } }, { "must": { "b2": "empty", "c3": "enemy" } }],
      "d2": [{ "must": { "c1": "empty", "d2": "empty" } }, { "must": { "c1": "empty", "d2": "enemy" } }]
    }
  }
}

L-shape via orthogonal step then diagonal step. Blockable: leg square must be empty.

First step	Leg	Destinations
North	`(file, rank+1)`	`(file-1, rank+2)`, `(file+1, rank+2)`
South	`(file, rank-1)`	`(file-1, rank-2)`, `(file+1, rank-2)`
East	`(file+1, rank)`	`(file+2, rank+1)`, `(file+2, rank-1)`
West	`(file-1, rank)`	`(file-2, rank+1)`, `(file-2, rank-1)`

5.8 Chariot

{
  "X:R": {
    "a1": {
      "a4": [
        { "must": { "a2": "empty", "a3": "empty", "a4": "empty" } },
        { "must": { "a2": "empty", "a3": "empty", "a4": "enemy" } }
      ]
    }
  }
}

Any number of squares orthogonally (like Chess Rook). Path must be clear.

5.9 Soldier (before river)

{
  "X:S": {
    "e3": {
      "e4": [{ "must": { "e4": "empty" } }, { "must": { "e4": "enemy" } }]
    }
  }
}

One square forward only. Crossing river mutates S → +S.

5.10 Soldier (after river)

{
  "X:+S": {
    "e5": {
      "d5": [{ "must": { "d5": "empty" } }, { "must": { "d5": "enemy" } }],
      "e6": [{ "must": { "e6": "empty" } }, { "must": { "e6": "enemy" } }],
      "f5": [{ "must": { "f5": "empty" } }, { "must": { "f5": "enemy" } }]
    }
  }
}

One square forward or sideways. Cannot move backward.

6. Special Move Notation

Encoded in PMN.

Move	PMN	Description
River crossing	`e4-e5`	Soldier crosses river, mutates S → +S
Soldier promotion	`e8-e8/E`	Soldier on last rank promotes to Empress
Face-to-face	`e4~e4`	Both Generals transform to Dragons

6.1 Face-to-face transformation

When both Generals occupy the same file with no pieces between them, both immediately transform to Dragons:

G^ → D^
g^ → d^

This is triggered by any move creating the alignment (General move or intervening piece removal).

6.2 Soldier promotion

When a Soldier ends a move on the last rank (rank 8 for South, rank 1 for North), promotion is optional. Choices:

Promotion	Result
Empress	`E` / `e`
Advisor	`A` / `a`
Cannon	`C` / `c`
Chariot	`R` / `r`
Bear	`B` / `b`
Horse	`H` / `h`

Promotion to General or Dragon is forbidden.

7. Termination

Status values from CGSN with game-specific interpretation.

7.1 Decisive

CGSN Status	Result
`mareking`	Terminal Piece (General or Dragon) captured → capturing player wins
`stalemate`	No legal move → active player loses
`resignation`	Resigning player loses
`repetition`	Player causing repetition loses

7.2 Draw

CGSN Status	Condition
`insufficient`	Both sides have only their Terminal Piece remaining
`movelimit`	50 moves without capture or Soldier move

8. Constraints

Rules transforming pseudo-legal moves (GGN) into legal moves.

8.1 No check constraint

Responding to check is not mandatory. A player may leave their Terminal Piece (General or Dragon) in check. If the Terminal Piece is captured, the game ends immediately.

8.2 Stalemate is loss

Unlike Chess, having no legal move results in a loss for the active player.

8.3 Repetition

A move is illegal if it:

Uses the same piece
From the same origin
To the same destination
With the same promotion choice (if applicable)
AND produces an identical position to one that occurred previously

Position identity includes:

All piece positions
Active player

The player committing such repetition loses immediately.

8.4 No drops

Captured pieces are stored in Hand but cannot be dropped back onto the Board.

9. Reference

Xiongqi rules page

10. License

Open Web Foundation Agreement 1.0 (OWFa 1.0) — OWFa 1.0