/* File:      fib.P
** Author(s): Jiyang Xu, Kostis Sagonas
** Contact:   xsb-contact@cs.sunysb.edu
** 
** Copyright (C) The Research Foundation of SUNY, 1986, 1993-1998
** 
** XSB is free software; you can redistribute it and/or modify it under the
** terms of the GNU Library General Public License as published by the Free
** Software Foundation; either version 2 of the License, or (at your option)
** any later version.
** 
** XSB is distributed in the hope that it will be useful, but WITHOUT ANY
** WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
** FOR A PARTICULAR PURPOSE.  See the GNU Library General Public License for
** more details.
** 
** You should have received a copy of the GNU Library General Public License
** along with XSB; if not, write to the Free Software Foundation,
** Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
** $Id: fib.P,v 1.1.1.1 1998/11/05 17:00:58 sbprolog Exp $
** 
*/


:- export demo/0.

demo :- 
	write('Enter N : '), read(N), nl, 
	fib(N, Fib), 
	write('Fib of '), write(N), write(' is '), writeln(Fib).

fib(N, X) :- fib0(N, X, _).

/* fib0(+Arg, -Result, -MinusOneRes) */

fib0(0, 1, 0).
fib0(1, 1, 1).
fib0(N, X, X1) :- 
	N > 1,
	N2 is N - 2,
	fib0(N2, X2, X3),
	X1 is X2 + X3,
	X is X1+X2.