reserve a,b,c,x,y,z for object,X,Y,Z for set,
  n for Nat,
  i,j for Integer,
  r,r1,r2,r3,s for Real,
  c1,c2 for Complex,
  p for Point of TOP-REAL n;

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;
