reserve i, n for Nat,
  x, y, a for Real,
  v for Element of n-tuples_on REAL,
  p, p1, p2, p3, q, q1, q2 for Point of TOP-REAL n;

theorem Th28:
  |(p+q, p+q)| = |(p, p)| + 2*|(p, q)| + |(q, q)|
proof
  |(p, p)| + |(p, q)| + |(p, q)| = |(p, p)| + 2*|(p, q)|;
  hence thesis by Th26;
end;
