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;

theorem Th3:
  for F being strict RingMorphism holds F is Morphism of dom(F),cod
  (F) & dom(F) <= cod(F)
proof
  let F be strict RingMorphism;
  ex G,H st G <= H & dom(F) = G & cod(F) = H & F is Morphism of G,H by Lm6;
  hence thesis;
end;
