Potential Chess

All pieces start out with the potential to be any piece. After a piece moves, its potential must be reduced (if necessary) according to the specific move it has made.

Rules

• Rules of orthodox chess apply except as follows.

• Whenever a piece is captured, the owning player must state which actual piece was captured. Depending on which actual piece was captured, all the other player's pieces are reduced to insure that no more than the standard number of chess pieces are retained (for example, once an actual Queen is captured, none of the other pieces has the potential to be a Queen any longer, so their Queen potentiality is removed).

• Castling, promotion and en passant as in normal chess except:

• Pawns promote to !KP (a piece which is neither a King nor a pawn). If a piece that is potentially a pawn, makes a pawn move to the last rank, the moving player must decide at that point whether to reduce the piece to a pawn and promote it, or reduce the piece to a non-pawn.

• Pawns or potential pawns on the 1st rank may make an initial two-square move. A potential pawn piece may be captured en passant. In this case, the captured piece is reduced to an actual pawn.

• Bishops must actualize onto different colored squares.

• Potential King pieces that are left in check immediately reduce so that they are no longer potential Kings. If all potential Kings are in check, the player must make a move such that at least one of them is no longer in check. A position in which all a player's potential Kings are in check, and there is no move that frees at least one of them from check is check mate.

• A player may not reduce a piece unless the reduction is forced (ie. by one of the above rules).

• Once a piece loses a potential, it is never regained.

At the end of the game, it should be possible to actualize all remaining pieces, and then, determining the starting array with the actual pieces, re-play the game as a orthodox chess game (albeit from a non-standard starting array).

Notation

coord1-coord2>piece1

   piece at coord1 moves to coord2 and is reduced to piece1

coord1:coord2>piece1(piece2)

   piece at coord1 captures piece at coord2 and is reduced to piece1. 
   captured piece is actualized into (piece2)


X   = any piece (ie. KQBRNP)
!K  = any piece except King (ie. QBRNP)
ABC = Potential to be an "A", "B" or "C"
!AB = Potential to be any piece except an "A" or "B"

Initial Array

   +---+---+---+---+---+---+---+---+
 8 | x | x | x | x | x | x | x | x |
   +---+---+---+---+---+---+---+---+
 7 | x | x | x | x | x | x | x | x |
   +---+---+---+---+---+---+---+---+
 6 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 5 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 4 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 3 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 2 | X | X | X | X | X | X | X | X |
   +---+---+---+---+---+---+---+---+
 1 | X | X | X | X | X | X | X | X |
   +---+---+---+---+---+---+---+---+
     a   b   c   d   e   f   g   h

Example moves

1. d2-d4>QRP     a7-b5>n

   +---+---+---+---+---+---+---+---+
 8 |!k | x | x | x | x | x | x | x |
   +---+---+---+---+---+---+---+---+
 7 |   |!k |!k |!k |!k |!k |!k |!k |
   +---+---+---+---+---+---+---+---+
 6 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 5 |   | n |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 4 |   |   |   |QRP|   |   |   |   |
   +---+---+---+---+---+---+---+---+
 3 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 2 |!K |!K |!K |   |!K |!K |!K |!K |
   +---+---+---+---+---+---+---+---+
 1 | X | X | X | X | X | X | X | X |
   +---+---+---+---+---+---+---+---+
     a   b   c   d   e   f   g   h

After

1. d2-d4>QRP

1. ... a7-b5>n

2. d1-d2>!bn     h7-g5>n

   +---+---+---+---+---+---+---+---+
 8 |!kn|!n |!n |!n |!n |!n |!n |!kn|
   +---+---+---+---+---+---+---+---+
 7 |   |!kn|!kn|!kn|!kn|!kn|!kn|   |
   +---+---+---+---+---+---+---+---+
 6 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 5 |   | n |   |   |   |   | n |   |
   +---+---+---+---+---+---+---+---+
 4 |   |   |   |QRP|   |   |   |   |
   +---+---+---+---+---+---+---+---+
 3 |   |   |   |   |   |   |   |   |
   +---+---+---+---+---+---+---+---+
 2 |!K |!K |!K |!bn|!K |!K |!K |!K |
   +---+---+---+---+---+---+---+---+
 1 | X | X | X |   | X | X | X | X |
   +---+---+---+---+---+---+---+---+
     a   b   c   d   e   f   g   h

After

d1-d2>!bn

1. ... h7-g5>n