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 Th19:
  for f being real-valued FinSequence st Sum f <> 0 holds Sum (f (/) Sum f) = 1
  proof
    let f be real-valued FinSequence;
    Sum (f (/) Sum f) = Sum f / Sum f by RVSUM_1:87;
    hence thesis by XCMPLX_1:60;
  end;

Lm6:
