proposition: Lemma is_ball_closure (A : set R) : is_ball A -> closure A = closed_ball (cpoint A) (radius A)%:num.
proof: Proof. by move=> ballA; rewrite /closed_ball -ballE. 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