-(*
-val union_list : Naive_tree.t ->Naive_tree.node list -> Naive_tree.node list -> Naive_tree.node list
-(** union two lists without duplicating
-*)
-
-val inter_list : Naive_tree.t ->Naive_tree.node list -> Naive_tree.node list -> Naive_tree.node list
-(** make a list without duplicating by using the intersection of two lists
-*)