theorem
  cl_Ball(p,r) = ClosedHyperInterval(@p - (n|-> r), @p + (n|-> r))
  proof
    reconsider q = p as Point of TOP-REAL n by EUCLID:22;
    ex a be Element of REAL n st a = p &
      ClosedHypercube(q,n |-> r)
        = ClosedHyperInterval(a - (n |-> r),a + (n |-> r)) by Th52;
    hence thesis by Th70;
  end;
