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,g being eventually-nonnegative Real_Sequence holds f in Big_Oh(g
  ) & g in Big_Oh(f) iff Big_Oh(f) = Big_Oh(g) by Lm5;
