reserve X for set;
reserve UN for Universe;

theorem
  for UN being non trivial Universe, n being Nat holds REAL n in UN
  proof
    let UN be non trivial Universe;
    let n be Nat;
    REAL is Element of UN & n-tuples_on REAL = REAL n by EUCLID:def 1,Th53;
    hence thesis by Th58;
  end;
