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% Factorial
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-module(facs).
-export([fac1/1]).
-export([fac2/1]).
-export([fac3/1]).

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% -- Public -- 
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fac1(N) -> N * fac1(N-1);
fac1(0) -> 1.

fac2(0) -> 1;
fac2(N) -> N * fac2(N-1).

fac3(N) when (N >  0) -> N * fac3(N-1);
fac3(N) when (N =< 0) -> 1.


%
% -- Private -- 
%