Proof [x,y,z:A][H:(Rstar x z)][H0:(Rstar y z)][P:Prop]
[H1:(z0:A)(Rstar x z0)->(Rstar y z0)->P](H1 z H H0).

Lemma Diagram:
(x:A)((u:A)(R x u)->(y:A)(z:A)(Rstar u y)->(Rstar u z)->(coherence y z))
->(y,z,u:A)(R x u)->(Rstar u y)
->(v:A)(R x v)->(Rstar v z)->(coherence y z).