+let rec fill_hashtag t =
+ if Tree.Binary.is_node t then
+ begin
+ let tag = Tree.Binary.tag t in
+ let a =
+ if TagSet.mem tag poa
+ then 0
+ else
+ fill_hashtag (Tree.Binary.first_child t)
+ in
+ let b = fill_hashtag (Tree.Binary.next_sibling t)
+ in a+b+1
+ end
+ else 0
+