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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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