proposition: Lemma ballxx (x : M) (e : R) : 0 < e -> ball x e x.
proof: Proof. by move=> e_gt0; apply: ball_center (PosNum e_gt0). Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed