proposition: Lemma precoeff_cons x s y k : precoeff x ((k, y) :: s) = (y == x)%:R * k + precoeff x s.
proof: Proof. by rewrite [LHS]big_cons /=; case: eqP; rewrite !simpm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)