:- module(_, [fib/2], []).
:- use_package(clpr).

fib(X,Y):- X .=. 0, Y .=. 0.
fib(X,Y):- X .=. 1, Y .=. 1.
fib(N,F) :-
    N .>. 1,
    N1 .=. N - 1,
    N2 .=. N - 2,
    fib(N1, F1),
    fib(N2, F2),
    F .=. F1+F2.
