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 Th17:
  Z_3 in RingObjects(UN)
proof
  ex x being object st x in UN & GO x,Z_3 by Th16;
  hence thesis by Def16;
end;
