proposition: Lemma opp_seqK l :opp_seq (opp_seq l) = l.
proof: Proof. by rewrite/opp_seq -map_comp; apply map_id_in => a /=; rewrite opprK. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice fintype order) mathcomp(binomial bigop ssralg poly ssrnum ssrint rat) mathcomp(polyrcf) pol