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 n being Nat st n >= 1 holds
    (2 to_power (n+1)) - (2 to_power n) > 1 by Lm48;
