proposition: Lemma nbhs_E {T T'} (ent : set_system (T * T')) x : nbhs_ ent x = filter_from ent (fun A => to_set A x).
proof: Proof. by []. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed