proposition: Lemma mxsub_eq_id f g : f =1 id -> g =1 id -> mxsub f g =1 id.
proof: Proof. by move=> fid gid A; rewrite (eq_mxsub fid gid) mxsub_id. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)