/*-----------------------------------------------------------------------------
  Fibonacci numbers
-----------------------------------------------------------------------------*/

ffib(0,0).
ffib(1,1).
ffib(M,N) :-
    M > 1, 
    M1 is M-1, 
    M2 is M-2,
    ffib(M1,N1), 
    ffib(M2,N2),
    N is N1+N2.
