type (a',b') Tree=Lead of a'| Noeud of b'*a'*(a',b')Tree list
 type strTree= st of int | Leaf of String | Tree of string *Strin* strTree list
 val Tree-strTree :(a'->string)->(b'->string)->(a',b')Tree -> strTree

 let Tree-strTree p pp a=
   let convert=fun x -> string_of_int x
   let rec mapA convert a' =match a' with
    | Lead _ -> Tree ("","",[])
    | Noeud (f,r,l)-> Tree(convert (p f),convert(pp r) ,
                        map(fun y->mapA convert y)l)
   in
  mapA convert a