let rec raices = function
            [] -> []
        |   Vacio::t -> raices t
        |   (Nodo(r,_,_))::t -> r::(raices t);;


let rec nodos = function
            [] -> []
        |   Vacio::t -> nodos t
        |   (Nodo(_,izq,der) -> izq::der::(nodos t);;

let anchura a =
        let rec aux = function
                [] -> []
            |   l -> (raices l)@(aux(nodos l))
        in aux[a];;