Ltac Esimpl :=
  repeat (progress (
   match goal with
   | |- context [?P@?l] =>
       match P with
       | P0 => rewrite (Pphi0 l)
       | P1 => rewrite (Pphi1 l)
       | (mkPX ?P ?i ?n ?Q) => rewrite (mkPX_ok l P i n Q)
       end
   | |- context [[?c]] =>
       match c with
       | 0 => rewrite ring_morphism0
       | 1 => rewrite ring_morphism1
       | ?x + ?y => rewrite ring_morphism_add
       | ?x * ?y => rewrite ring_morphism_mul
       | ?x - ?y => rewrite ring_morphism_sub
       | - ?x => rewrite ring_morphism_opp
       end
   end));
  simpl; rsimpl.

Lemma PmulC_aux_ok : forall c P l, (PmulC_aux P c)@l == P@l * [c].