specialised fact in the Record theory should not be appear in proofs discovered by sledgehammer
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;