anchor.diff:  /// Minimum value for time instants.
   const int _alpha = -_omega;
   
  -LocationDatabase filterTimeZoneData(LocationDatabase db, {int dateFrom: _alpha,
  -    int dateTo: _omega}) {
  +Tuple2<LocationDatabase, Report> filterTimeZoneData(LocationDatabase db,
  +    {int dateFrom: _alpha, int dateTo: _omega}) {
  +  final report = new Report();
     final result = new LocationDatabase();
  +
  +  report.originalLocationsCount = db.locations.length;
   
     for (final l in db.locations.values) {
       final transitionsCount = l.transitionAt.length;
  +    report.originalTransitionsCount += transitionsCount;
  +
       final newTransitionAt = [];
       final newTransitionZone = [];
   
  
positive.code: 
      result.add(
          new Location(l.name, newTransitionAt, newTransitionZone, l.zones));
    }
  
    return result;
  }
  
  void main(List<String> arguments) {
  
negative.code:   }
  
    initializeTimeZone(source).then((_) {
      final result = filterTimeZoneData(LocationDatabase.instance,
          dateFrom: from,
          dateTo: to);
  
      final newDB = result.i1;
      final report = result.i2;
  
      return new File(output).writeAsBytes(newDB.toBytes()).then((_) {
        print('Locations: ${report.originalLocationsCount} => ${report.newLocationsCount}');
        print('Transitions: ${report.originalTransitionsCount} => ${report.newTransitionsCount}');
        exit(0);
      });
  
  