%fib(0, 0). %fib(1, 1). %fib(X, Y) :- X > 1, X2 is X – 2, fib(X2, Y2), X1 is X – 1, fib(X1, Y1), Y is Y1 + Y2. fib(0, 0). fib(1, 1). fib(X, Y) :- X > 1, X1 is X - 1, X2 is X - 2, fib(X1, Y1), fib(X2, Y2), Y is Y1 + Y2.