theorem Th25:
  for p being Point of TOP-REAL 3 holds
  Sum sqr p = p`1^2+p`2^2+p`3^2
  proof
    let p be Point of TOP-REAL 3;
    p = |[ p`1, p`2, p`3 ]| by EUCLID_5:3;
    hence thesis by Th16;
  end;
