% | 1 | 2 | 3 |
% | 4 | 5 | 6 |
% | 7 | 8 | 9 |

bishop(1,5).
bishop(2,4).
bishop(2,6).
bishop(3,5).
bishop(4,8).
bishop(5,7).
bishop(5,9).
bishop(6,8).

bishopbi(X,Y):-bishop(X,Y);
               bishop(Y,X).

move_user(X,Y) :- retractall(visited(Z)),
	          asserta(visited(X)),
	          asserta(visited(Y)),
	          move(X,Y).

move(X,Y) :- bishopbi(X,Y).
move(X,Y) :- bishopbi(X,Z),
	     not(visited(Z)),
	     asserta(visited(Z)),
	     print(Z),nl,
	     move(Z,Y).