src/HOL/SPARK/Manual/document/Gcd.ads

treat map_filter similar to list_all, list_ex, list_ex1

package Greatest_Common_Divisor
is

   --# function Gcd(A, B: Natural) return Natural;

   procedure G_C_D(M, N: in Natural; G: out Natural);
     --# derives G from M, N;
     --# pre M >= 0 and N > 0;
     --# post G = Gcd(M,N);

end Greatest_Common_Divisor;