intros U R; red in |- *.
intros x y H'; elim H'.
generalize Rstar_contains_R; intro T; red in T; auto.
intros x0 y0 z H'0 H'1 H'2; apply Rstar_n with y0; auto.
Qed.

Theorem Rstar_transitive :
forall (U : Type) (R : Relation U), Transitive U (Rstar U R).