sig
type 'a t = Empty_tree | Node of 'a * 'a Tree.t list
exception Empty_forest
val sons : 'a Tree.t -> 'a Tree.t list
val nth : int -> 'a Tree.t -> 'a Tree.t
val label : 'a Tree.t -> 'a
val to_string : 'a Tree.t -> ('a -> string) -> string
val to_xml : 'a Tree.t -> ('a -> string) -> string
val read : string -> (string -> 'a) -> 'a Tree.t
end