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

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

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

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