Chess Variants/Circe Chess

Introduction
Circe Chess is a variant that allows for pieces to be reborn after capture.

History
Circe chess was created by French composer Pierre Monréal, who described the rules in an article in Problème magazine the following year. The variant is named after the Greek goddess Circe, and is rarely played as an actual game. It is more often used for fairy puzzles.

Rules
Circe chess is played mostly like the standard game, with one key difference: when a piece is captured it is not removed from the board, but rather it is immediately reborn on its starting square. To be more specific:


 * Pawns are reborn on the starting square on the file they are on.
 * Rooks, knights and bishops are reborn on the starting square that matches the colour of the square the piece was on when it was captured.

However, if the square the piece would be reborn on is occupied by another piece, whether friendly or hostile, then the piece is not reborn and is instead removed from the board as in standard chess.

If a pawn is captured via en passant, it will immediately be reborn on the square in front of the opponent's pawn, preventing either pawn from moving.

Sub-variants
There are many sub-variants of Circe chess, usually differing oin where captured pieces are reborn. Wikipedia lists the following:


 * Anticirce: The capturing piece is reborn on its initial square. The captured piece disappears from the board. The rebirth square must be empty or the capture is illegal. There are two types: Type Cheylan: captures on the rebirth square are illegal (i.e. a white rook can not capture on a1). Type Calvet: captures on the rebirth square are legal.
 * Assassin Circe: The rebirth occurs even if the rebirth square is occupied. The occupying piece is removed from the board. When a piece is captured on its rebirth square, the capturing piece disappears.
 * Chamaeleon Circe: A captured piece (other than a pawn) is reborn as a different piece: knight becomes bishop, bishop becomes rook, rook becomes queen and queen becomes knight. The reborn piece is placed according to the Circe rule for the new piece.
 * Circe Parrain: A captured piece is reborn on the square displaced from the capture square by a vector equal to that of the move following the capture. If the following move is castling, then the sum of the king-move and rook-move vectors is used (for a kingside castle, rebirth can occur only if the piece is a pawn captured en passant).
 * Circe Rex inclusive: As Circe, but also the kings may be captured. A mate requires that the initial square of the king is occupied.
 * Clone Circe: A captured piece is reborn on its initial square but reappears as the piece by which it is captured (not a king).
 * CouCou Circe: As Circe, but the rebirth square is that of the capturing piece. Pawns captured by a piece are reborn on the promotion rank, and promote. The promotion is chosen by the capturing side.
 * CousCous Circe: As CouCou Circe, but for captures resulting in promotion, the promotion type is chosen by the side whose pawn promotes.
 * Diagram Circe: A captured piece is reborn on the position it had on the diagram.
 * Equipollents Circe: As Circe Parrain, but the rebirth occurs immediately on a vector equal to the capturing move.
 * Kamikaze Circe: The captured piece is reborn on its initial square. The capturing piece disappears.
 * Martian Circe: Pieces move in the ordinary manner but capture only from their initial position (if it is unoccupied). Captured pieces disappear from the board.
 * Mirror Circe: A captured piece is reborn on a square where a piece of the opposite colour would be reborn in ordinary Circe.
 * Platzwechsel Circe (PWC): A captured piece is reborn on the square where the capturer was placed before the capture. Platzwechsel means "position exchange" in German.
 * Strict Circe: As ordinary Circe, but the rebirth square must be free for the capture to be legal.
 * Symmetrical Circe: As Circe, but the rebirth square is the capture square mirrored across the center of the board.
 * Volcanic Circe: As Circe, but if the rebirth square is occupied, the captured piece is 'hidden' under that piece. When that piece moves, the hidden piece is revealed. E.g. white king on f1, white bishop on a6, black king on b6: Black captures Kb6xa6(+wBf1(hidden)) Kf1-e1 (+wBf1).