Fixpoint power (base : nat) (exp : nat) : nat :=
 match exp with
 | 0 => 1
 | S n => base * (power base n)
 end.

Lemma countBLeafCT_mono_diff: forall n1 n2 s1 s2, n1 <= n2 -> (s1 <= s2)%ba -> countBLeafCT n1 s2 - countBLeafCT n1 s1 <= countBLeafCT n2 s2 - countBLeafCT n2 s1.