Theorem Rstar'_R: (x:A)(y:A)(z:A)(R x z)->(Rstar z y)->(Rstar' x y).
Proof [x,y:A]
[z:A]
[t1:(R x z)]
[t2:(Rstar z y)]
(unf_Rstar' [P:A->A->Prop](P x y)
[P:A->A->Prop]
[_:(P x x)][h2:(u:A)(R x u)->(Rstar u y)->(P x y)](h2 z t1 t2)).