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;
reserve n for non zero Nat;

theorem
  ProductRightOpenIntervals(n) = Seg n --> the set of all [.a,b.[ where
    a,b is Real;
