let make_graph entree result = (* ent : in; res :out *)
  let lengthRes = String.length result in
  let rec aux deb fin graph=
    match deb=fin with
    |true -> if deb=lengthRes then graph else aux 0 (fin+1) graph
    |false->
       let edge = make_edge entree (String.sub result deb fin) in
       aux (deb+1) fin (((deb,fin),edge)::graph)
  in aux 0 1 []