intros U R S H'.
apply Sstar_contains_Rstar.
generalize (Rstar_contains_R U S); auto.
Qed.

Theorem RstarRplus_RRstar :
forall (U : Type) (R : Relation U) (x y z : U),
Rstar U R x y -> Rplus U R y z -> exists u : U, R x u /\ Rstar U R u z.