Chess Variants/Alice Chess

Introduction
Alice chess is a variant where pieces teleport between two boards.

History
Alice chess was created by prolific chess variant creator V. R. Parton in 1953. The variant is inspired by the Lewis Carroll book Through the Looking-Glass, the sequel to Alice's Adventures in Wonderland. The book involves Alice stepping through a looking-glass and entering a fantastical world, which translates into the variant's main mechanic. Indeed, the variant itself is named after Alice.

Rules
As already stated Alice chess is played with two boards, designated with the letters A and B, laid next to each other at game start. All of the pieces begin the game on board A.

On each turn, a player may choose to move a piece on either board A or B. The piece all retain their typical moves, but once a piece completes its move, it goes "through the looking-glass" and is teleported to the corresponding square on the opposite board. So for example, if a white knight moved from f1 to g3 on board A, would then be teleported to the g3 square on board B.

There are two basic stipulations concerning each move:


 * The move must be legal on the board where it is played.
 * The corresponding square on the opposite board cannot be occupied by another piece, friendly or hostile.

Captures may only be played on the same board that the piece is moving on, since the teleport happens after the piece's move is complete.

When moving on one board a piece is allowed to pass over squares that are occupied by pieces on the other board. For example, in the diagram at left, after White moved Black would be allowed to play 3... Bg1, despite there being a white pawn on f2 on board A, since the move is legal on board B and g1 on square A is unoccupied.

The king is not allowed to make a move on one board, if his teleport to the other board would land him in check. He is also not allowed to use the teleport to escape check - he must move out of check before the teleport. Additionally, you may not make a capture if your piece's teleport would expose your king to check.

You are allowed to escape check by moving a piece on the other board so that its teleport blocks the check.

Castling is permitted as in standard chess, with both the king and rook teleporting to the other board.

There is no en passant.

Sub-variants

 * In Looking-glass Alice chess, the white pieces start on board A as usual, but the black pieces start on board B.
 * Ms. Alice chess allows a player to make a null move, which simply teleports a piece to the other board without moving it.
 * In O'Donohue chess you are allowed to move a piece to a square occupied on the other board - in whcih case the teleport portion of the move is skipped.
 * As its name suggests, Three-board Alice chess uses three boards instead of two. You are allowed to selected which board your piece teleports to.