Section Relations.
(* Properties of a binary relation R on type A *)
Variable A : Set.
Variable R : A -> A -> Prop.
(* Definition of the reflexive-transitive closure R* of R *)
(* Smallest reflexive P containing R o P *)
Definition Rstar (x y : A) :=
forall P : A -> A -> Prop,
(forall u : A, P u u) ->
(forall u v w : A, R u v -> P v w -> P u w) -> P x y.

Theorem Rstar_reflexive : forall x : A, Rstar x x.