proposition: Lemma open_nbhs_closed_ball (R : realType) (V : normedModType R) (x : V) (r : R) : 0 < r -> open_nbhs x (closed_ball x r)^°.
proof: Proof. move=> r0; split; first exact: open_interior. by rewrite interior_closed_ballE //; exact: ballxx. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg ssrint ssrnum finmap matrix) mathcomp(rat interval zmodp vector fieldext falgebra) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality set_interval Rstruct) ereal reals signed topology prodnormedzmodule