% From the book
% PROLOG PROGRAMMING IN DEPTH
% by Michael A. Covington, Donald Nute, and Andre Vellino
% (Prentice Hall, 1997).
% Copyright 1997 Prentice-Hall, Inc.
% For educational use only

% File FACTORIA.PL
% Given an integer, finds its factorial.

factorial(0,1) :- !.

factorial(N,FactN) :-
  N > 0,
  M is N-1,
  factorial(M,FactM),
  FactN is N*FactM.