reserve x,y for set;
reserve D for non empty set;
reserve UN for Universe;
reserve f for RingMorphismStr;
reserve G,H,G1,G2,G3,G4 for Ring;
reserve F for RingMorphism;
reserve V for Ring_DOMAIN;

theorem
  for f being Morphism of G,H holds {f} is RingMorphism_DOMAIN of G,H
proof
  let f be Morphism of G,H;
  for x being Element of {f} holds x is Morphism of G,H by TARSKI:def 1;
  hence thesis by Th13;
end;
