We say that a set of rooks dominate the chessboard if each square is either occupied by a rook, or can be directly attacked by a rook. Obviously the smallest number of rooks which can dominate a chessboard is 12, which we can achieve by placing them along the main diagonal.
In 3-dimensional chess, rooks can attack in a straight line in the direction of the coordinate axis. What is the minimum number of rooks which can dominate a chessboard?