Conversion Chess

Rules

The standard rules of co-Chess apply, except where explicitly stated as otherwise so.

The standard rules of Co-chess are:

1. The standard rules of chess apply except where stated.
2. In co-chess, each pair of identical pieces of the same colour (excluding pawns) forms a co-pair.
   Kings also form co-pairs with queens.
   Promoted pieces allow multipairing.
3. Whenever one member of a co-pair moves to a square not on the same rank or file as the other, the co-pair defines two co-squares, each on the same rank as one of the pieces and the same file as the other.
   Only a moving piece can form co-squares.
   Castling is both a king move and a rook move, so both pieces can form co-squares thereby.
4. Any piece on a co-square is subject to a co-effect.
   The nature of the co-effect defines the game being played.
   Co-effects are mandatory.
   A square is only a single move a co-square: after the move that formed the co-square, the co-effect is carried out, but not after that (but a square could become co-square multiple times).
   Pawn promotion cannot cause co-effects.
   Castling into check is permitted if the check is removed by means of the co-effect.

1. The co-effect in conversion chess is conversion: any enemy piece on a co-square is converted to a friendly piece of the same type.
2. Friendly pieces are unaffected.
3. Conversion of a piece does not cause further conversion.
4. A threat to convert the King is check. This works exactly the same as regular check with respect to guarded squares, checkmate, and stalemate. Regular check exist too, of course.

Sample games

Piero Pugnali - Alessandro Castelli (Grand Prix 1993) 0-1
1.Nf3?! d5 2.d4?? Bh3/Nf3+ 3.g:f3 Bg2/f2+ 4.Kd2 B:h1/Bf1 5.Q:f1/Pf2 Qd6 6.Q:h1 Qf4+ 7.Kd3 Qf5+ 8.Kc3 Nc6 9.e3 000+ 10.Resigns

Alessandro Castelli - Michele De Giglio (Grand Prix 1993) 1-0
1.e4 d6 2.d4 c6 3.Ag5 Qa5+?? 4.Ba6/Qa5 Resigns

Michele De Giglio - Alessandro Castelli (Grand Prix 1993) 0-1
1.e4 d5 2.c4 c6 3.c:d5 e5 4.Qh5/Pe5 Qa5/Pe5 5.Qg5+/Pe5 f6 6.e:f6 Kf7 7.f3?? Kg6/Qg5 8.Resigns