reserve n   for Nat,
        r,s for Real,
        x,y for Element of REAL n,
        p,q for Point of TOP-REAL n,
        e   for Point of Euclid n;
reserve n for non zero Nat;

theorem Th30:
  MeasurableRectangle(ProductLeftOpenIntervals(n)) is Semiring of REAL n
  proof
    MeasurableRectangle(ProductLeftOpenIntervals(n)) is Semiring of
      product ProductREAL(n) by SRINGS_4:40;
    hence thesis by Th7;
  end;
