Definition share_metric (n : nat) (s : canonTree) : nat :=
 match n with
 | 0 => 0
 | S n => match le_dec (height s) n with
          | left _ => countBLeafCT n s + 1
          | right _ => 0
         end
 end.

Lemma shareTreeOrd_dec: forall t1 t2 : ShareTree, {shareTreeOrd t1 t2} + {~shareTreeOrd t1 t2}.