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 x being Real st x > 9 holds 2 to_power x > (2*x)^2 by Lm31;
