reserve R for Ring, S for R-monomorphic Ring,
        K for Field, F for K-monomorphic Field,
        T for K-monomorphic comRing;

theorem
   for f being Monomorphism of R,S holds f" is one-to-one onto
   proof
     let f be Monomorphism of R,S;
     rng(f") = dom f by FUNCT_1:33 .= [#]R by FUNCT_2:def 1;
     hence thesis;
   end;
