prologs

/* fatorial recursivo */
fatorial(1,1) :- !.
fatorial(N,F):- X is N-1,
                fatorial(X, Y),
                F is N*Y,
                !.


/* exercício 1 - fibonacci */
fib(1,0) :- !.
fib(2,1) :- !.
fib(N,F) :- X is N-1,
            Y is N-2,
            fib(X,A),
            fib(Y,B),
            F is A+B,
            !.


/* exercício 2 - número natural */
nat(X) :- positivo(X),
          A is round(X),
          A =:= X.

positivo(X) :- X > 0.