Adventures in Prolog - Fibonacci

As I have played around with Prolog lately, I wanted to share some enriching moments with my new favourite pet. We start of with the famous Fibonnaci numbers and their computation in Prolog. To spice things up, I used the dynamic clause, which enables one to add clauses to an existing database.

:- dynamic(fib/2).
fib(0, 1).
fib(1, 1).
fib(F, X) :-
  F1 is F-1,
  F2 is F-2,
  fib(F1, X1),
  fib(F2, X2),
  X is X1 + X2,
  asserta(fib(F, X)).


So what does this listing do? Clearly, it computes the ith value of the Fibonacci sequence using recoursion. Therefore, the recoursion anchor - 1st and 0th value - of the sequence is established first. After that the definition of the sequence is given in its known form.
By making the predicate fib/2 dynamic, we can add facts to the list of clauses covering fib/2. Dynamic has to be executed upon loading the fib database. That is why we write :- dynamic(fib/2). .
Now new knowledge about the Fibonnaci values can be added to the database. This is what is done later one with the asserta statement - asserta adds new clauses at the beginning of the database (assertz at the end). The value of the computation of the jth Fibonacci sequence value (fib(J, X)) is added as a fact to the database, thereby speeding up future computations of the same Fibonacci sequence value.