Slide-chess

Setup

setup:  [],() are cages that slide around the board (check rules)
        
        [] -> White cage
        () -> Black cage (notice they begin at the player's last row)

8        [ ]        
7   r n b k b n r   
6   p p p p p p p              
5   . . . . . . .
4   . . . . . . .
3   O O O O O O O
2   R N B K B N R
1        ( )
  a b c d e f g h i

1. FIDE rules, except:
2. On each move, each player must do one of:
   1. make a regular Chess move, which includes moving or capturing into or out of either cage.
   2. move his cage (with any contents) to any empty edge or corner (orthogonally or diagonally) adjacent to a square board; b1: It is illegal to check the enemy King with a cage move b2: A player may not move his cage twice consecutively.
   3. insert his cage (with any contents) orthogonally into the board, shifting the other cells in line until a cage appears at the opposite edge (which must have been empty).

   Eg:
          [ ]
     r . b k b n r
     p p p p . p p
     . . O . p . .(n)
     . . . . . . .
     O O . O O O O
     R N B K B N R
              
   
   becomes:
           [ ]
      r . b k b n r
      p p p p . p p
   ( ). O . p . . n 
      . . . . . . .
      O O . O O O O
      R N B K B N R
        

3. No double initial pawn step; no castling.
4. When a pawn reaches the 2nd/7th rank, the mover decides how it promotes (the pawn may promote to a Queen).
5. No king must ever be in a cage.