reserve
  x, y for object,
  i, n for Nat,
  r, s for Real,
  f1, f2 for n-element real-valued FinSequence;

theorem Th6:
  Family_open_set(Euclid 0) = {{},{{}}}
  proof
    the TopStruct of TOP-REAL 0 = TopSpaceMetr Euclid 0 by EUCLID:def 8;
    hence thesis by EUCLID:77,YELLOW_9:9;
  end;
