reserve c, c1, c2, d, d1, d2, e, y for Real,
  k, n, m, N, n1, N0, N1, N2, N3, M for Element of NAT,
  x for set;

theorem
  for f being Real_Sequence, b being Real st f.0 = 0 & (for n st n > 0
  holds f.n = b) holds for N being Element of NAT holds Sum(f,N) = b*N by Lm14;
