proposition: Lemma nbhs_norm_ball_norm x (e : {posnum R}) : nbhs_norm x (ball_norm x e%:num).
proof: Proof. by rewrite ball_normE; exists e%:num => /=. 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