Instance mkPX_ext : Proper (Pequiv ==> eq ==> Pequiv ==> Pequiv) mkPX.(* Quicker than autorewrite with Esimpl :-) *)
 Ltac Esimpl := try rewrite_db Esimpl; rsimpl; simpl.

Lemma PmulI_ok P' : (forall P l, (Pmul P P') @ l == P @ l * P' @ l) -> forall P p l, (PmulI Pmul P' p P) @ l == P @ l * P' @ (jump p l).