proposition: Lemma mxdirect_trivial m n A : mxdirect (unwrap (@trivial_mxsum m n A)).
proof: Proof. exact: eqxx. 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 finalg zmodp matrix)