proposition: Lemma tail_correct n pi p : pi >:: p -> tail n pi >:: PolR.tail n p.
proof: Proof. move=> Hp k; rewrite /nth /PolR.nth. exact: (drop_correct (Rel := fun v t => t >: v)). Qed.
imports: Coq(ZArith Reals) Coquelicot(Coquelicot) mathcomp.ssreflect(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype bigop) Flocq(Core) Stdlib MathComp Interval Xreal Basic_rec