fact: Definition nbhs_ball_ {R : numDomainType} {T T'} (ball : T -> R -> set T') (x : T) := @filter_from R _ [set e | e > 0] (ball x).
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed