proposition: Lemma radius_ball x r (r0 : 0 <= r) : radius (ball x r) = NngNum r0.
proof: Proof. by apply/val_inj => //=; rewrite radius_ball_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