The Central Squares

All FIDE rules apply, except:

• The board is made of a three 6x6 boards, denoted by A, B and C. The 2x2 central squares of boards A and C are removed, just like in the next figure:

• The 2x2 central squares of B are linked also to A and C as if all 3 boards shared those same four squares. In a sense, if a piece stands in one of these squares, it lies on all boards. So for e.g., square Bc3 equals to Ac3 and Cc3. This way, we can denote the central squares without the board prefix (Cc3 becomes just c3). Notice that a rook movement can go from Ac1 to Bc6 (or Cc6) since it is possible to be transferred to a different board using the central squares.
• The initial setup is presented in the next figure:

• Piece 3D movements (I show the movements outside and inside the central squares)

• Rook: can also move up and down in rookwise fashion. For e.g., the rook in Aa1 can also move to Ba1 and Ca1.

• Bishop: can also move diagonals up and down. For e.g., the bishop in Ab1 can move to Ba2, Bc2 and d3. From d3, the bishop can go to Be4, Ce4 and Cf5 (from Be4).

• Knight: jump 2 squares (north/south, east/west or up/down) and then turn 90 degrees (there are 2 ways to turn 90 degrees in 3D) and move one square..

• Queen: Bishop + Rook

• King: can also move up/down.  There is no castling.

• Pawn: can also move 1 square up (for white) or down (for black) or capture east/west in up direction for white and down for black. For e.g., the pawn at Ab2 can move to Ab3 or Bb2, or capture to Aa3, c3 (typical) and also Ba2 and Bc2. There is no initial double move. White promotions occur in rank 6 of board C and black promotions in rank 1 of board A.