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

(*L55*)
Lemma tree_height_glb_limit: forall n s1 s2,
height s1 <= n ->
height s2 <= n ->
height (glb s1 s2) <= n.