allow negative int values as well, according to real = int | float;
package Simple_Greatest_Common_Divisoris --# function Gcd (A, B : Natural) return Natural; procedure G_C_D (M, N : in Natural; G : out Natural); --# derives G from M, N; --# pre N > 0; --# post G = Gcd (M, N);end Simple_Greatest_Common_Divisor;