fits(1). fits(2). fits(3). fits(4).
fits(5). fits(6). fits(7). fits(8).

solve(A,B,C,D,E,F,G,H) :-
    fits(A), fits(B), fits(C), fits(D),
    fits(E), fits(F), fits(G), fits(H),
    A \== B, A \== C, A \== D, A \== E, A \== F, A \== G, A \== H,
    B \== C, B \== D, B \== E, B \== F, B \== G, B \== H,
    C \== D, C \== E, C \== F, C \== G, C \== H,
    D \== E, D \== F, D \== G, D \== H,
    E \== F, E \== G, E \== H,
    F \== G, F \== H,
    G \== H,
    \+(A is B+1), \+(A is B-1), \+(A is C+1), \+(A is C-1),
    \+(A is D+1), \+(A is D-1), \+(A is E+1), \+(A is E-1),
    \+(B is D+1), \+(B is D-1), \+(B is E+1), \+(B is E-1),
    \+(B is F+1), \+(B is F-1),
    \+(C is D+1), \+(C is D-1), \+(C is G+1), \+(C is G-1),
    \+(D is E+1), \+(D is E-1), \+(D is G+1), \+(D is G-1),
    \+(D is H+1), \+(D is H-1),
    \+(E is F+1), \+(E is F-1), \+(E is G+1), \+(E is G-1),
    \+(E is H+1), \+(E is H-1),
    \+(F is H+1), \+(F is H-1),
    \+(G is H+1), \+(G is H-1).