proposition: Lemma map_mxB A B : (A - B)^f = A^f - B^f.
proof: Proof. by rewrite map_mxD map_mxN. 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)