reserve a,b,s,t,u,lambda for Real,
  n for Nat;
reserve x,x1,x2,x3,y1,y2 for Element of REAL n;

theorem :: EUCLID_2:21
  for x1,x2 being Element of REAL n,a being Real holds |(x1,a*x2
  )| = a*|(x1,x2)| by Th21;
