Conversion Chess Conversion chess has been invented in 1973 by Ralph Betza. The standard rules of co-Chess apply, except where explicitly stated as otherwise so. Kings also form co-pairs with queens.
Promoted pieces allow multipairing.
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. The nature of the co-effect defines the game being played. Co-effects are mandatory. Pawn promotion cannot cause co-effects.