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%%
%% 991202 Slim Abdennadher, LMU
%%
%% ported to hProlog by Tom Schrijvers

:- module(fib,[]).

:- use_module(library(chr)).

:- constraints fib/2.

%% fib(N,M) is true if  M is the Nth Fibonacci number.

%% Top-down Evaluation with Tabulation

fib(N,M1), fib(N,M2) <=> M1 = M2, fib(N,M1).

fib(0,M) ==> M = 1.

fib(1,M) ==> M = 1.

fib(N,M) ==> N > 1 | N1 is N-1, fib(N1,M1), N2 is N-2, fib(N2,M2), M is M1 + M2.