Module Pos2Nat.
(** [Pos.to_nat] is a morphism for successor, addition, multiplication *)
(** Mapping of xH, xO and xI through [Pos.to_nat] *)
(** [Pos.to_nat] maps to the strictly positive subset of [nat] *)
(** [Pos.to_nat] is strictly positive *)

Lemma is_pos p : 0 < to_nat p.