% Factorial in prolog
% This one remembers its values, ready for the next call...
:-dynamic(f/2).


f(1,1):-!.
f(N,_):-N=<0,!,fail.
f(N,F):-N1 is N-1,
	f(N1,F1),
	F is F1 * N,			
	print(N),write('!='), print(F), nl,
	Fact=.. [ :-, f(N,F),! ],
	asserta(Fact).