
theorem
  for x be Nat st 2 <= x holds 1 < LenBSeq x
  proof
    let x be Nat;
    assume
AS0:2 <= x; then
    consider n be Nat such that
P3: 2 to_power n <= x & x < 2 to_power (n + 1)
      & LenBSeq x = n+1 by BINARI_6:def 1;
    n <> 0 by AS0,P3; then
    0 + 1 < n+1 by XREAL_1:8;
    hence thesis by P3;
  end;
