Prevent backtracking after first solution to Fibonacci pair

Question

The term fib(N,F) is true when F is the Nth Fibonacci number.

The following Prolog code is generally working for me:

Answer 1

If you are only interested in the first solution or know that there is at most one solution, you can use once/1 to commit to that solution:

?- once(fib(X, 377)).

+1 for using CLP(FD) as a declarative alternative to lower-level arithmetic. Your version can be used in all directions, whereas a version based on primitive integer arithmetic cannot.