static Map<O, Set<S>> dm_ai_analyzeLineCategoryWithFeature_map(S category, fS feature) {
  LPair<O, S> pairs = map(objectsWhere(dm_lineToCategory_entries(), +category), func(Line2Category l) -> Pair<O, S> {
    pair(callAndMake(feature, l.line), l.answer)
  });
  ret pairsToMapWithSetValues(pairs);
}