proposition: Lemma precoeff_perm_eq x s1 s2 : perm_eq s1 s2 -> precoeff x s1 = precoeff x s2.
proof: Proof. by rewrite !precoeffE => /prelift_perm_eq ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)