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 Rstar_coherence : (x:A)(y:A)(Rstar x y)->(coherence x y).
Proof [x,y:A][h:(Rstar x y)](coherence_intro x y y h (Rstar_reflexive y)).