+type bitmap
+
+val bitmap_create : unit -> bitmap
+val bitmap_push_back : bitmap -> int -> unit
+
+
+type t
+
+val create : bitmap -> t
+external save : t -> Unix.file_descr -> unit = "caml_bp_save"
+external load : Unix.file_descr -> t = "caml_bp_load"
+external first_child : t -> int -> int = "caml_bp_first_child" "noalloc"
+external next_sibling : t -> int -> int = "caml_bp_next_sibling" "noalloc"
+external preorder_rank : t -> int -> int = "caml_bp_preorder_rank" "noalloc"
+