proposition: Lemma open_nbhs_ball (x : M) (eps : {posnum R}) : open_nbhs x ((ball x eps%:num)^°).
proof: Proof. split; first exact: open_interior. by apply: nbhs_singleton; apply: nbhs_interior; exact: nbhsx_ballx. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed