reserve X for set,
        n,m,k for Nat,
        K for Field,
        f for n-element real-valued FinSequence,
        M for Matrix of n,m,F_Real;

theorem Th9:
  for x be real-valued FinSequence
  holds 0 <= Sum abs x
  proof
    let x be real-valued FinSequence;
    |.(Sum x).| <= Sum(abs x) by TOPREALC:21;
    hence thesis;
  end;
