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

(*L47*)
Lemma countBLeafCT_join_eq: forall n s1 s2 s3,
join s1 s2 s3 ->
height s1 <= n ->
height s2 <= n ->
countBLeafCT n s1 + countBLeafCT n s2 = countBLeafCT n s3.