Section Clos_Refl_Sym_Trans.
(** Reflexive-transitive closure is included in the reflexive-symmetric-transitive closure *)
(** Reflexive closure is included in the reflexive-transitive closure *)

Lemma clos_rt_t : forall x y z,
clos_refl_trans R x y -> clos_trans R y z ->
clos_trans R x z.