proposition: Lemma mx_nbhs_nbhs M (A : set 'M[T]_(m, n)) : nbhs M A -> nbhs M (nbhs^~ A).
proof: Proof. move=> [P M_P sPA]; exists (fun i j => (P i j)^°). by move=> ? ?; apply: nbhs_interior. by move=> ? ?; exists P. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed