reserve a,b,i,j,k,l,m,n for Nat;

theorem
  for f be complex-valued FinSequence, x be Complex holds
    Sum (f-x) = Sum f - x*(len f)
   proof
     let f be complex-valued FinSequence, x be Complex;
     reconsider f as FinSequence of COMPLEX by RVSUM_1:146;
     Sum (f+-x) = Sum f + (-x)*(len f) by SFX;
     hence thesis by VALUED_1:def 3;
   end;
