Definition truncate_aux t k :=
  let '(m, e, l) := t in
  let p := Zpower beta k in
  (Zdiv m p, (e + k)%Z, new_location p (Zmod m p) l).

(* Specifications: *)
Theorem truncate_aux_comp : forall t k1 k2, (0 < k1)%Z -> (0 < k2)%Z -> truncate_aux t (k1 + k2) = truncate_aux (truncate_aux t k1) k2.