
theorem N2103:
  for D be set, f be Function holds
  f is D-valued iff f is Function of dom f,D
  proof
    let D be set, f be Function;
    thus f is D-valued implies f is Function of dom f,D
    proof
      assume f is D-valued; then
      rng f c= D by RELAT_1:def 19;
      hence thesis by FUNCT_2:2;
    end;
    thus thesis;
  end;
