proposition: Lemma fct_ball_center (x : T -> U) (e : R) : 0 < e -> fct_ball x e x.
proof: Proof. by move=> /posnumP[{}e] ?. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed