docs: def Lookup(self,
               keywords,
               start_time=FIRST_TIMESTAMP,
               end_time=LAST_TIMESTAMP,
               last_seen_map=None):
      """Finds objects associated with keywords.
  
      Find the names related to all keywords.
  
      Args:
        keywords: A collection of keywords that we are interested in.
        start_time: Only considers keywords added at or after this point in time.
        end_time: Only considers keywords at or before this point in time.
        last_seen_map: If present, is treated as a dict and populated to map pairs
          (keyword, name) to the timestamp of the latest connection found.
      Returns:
        A set of potentially relevant names.
  
      """
      posting_lists = self.ReadPostingLists(
          keywords,
          start_time=start_time,
          end_time=end_time,
          last_seen_map=last_seen_map)
  
      results = list(itervalues(posting_lists))
      relevant_set = results[0]
  
      for hits in results:
        relevant_set &= hits
  
        if not relevant_set:
          return relevant_set
  
      return relevant_set