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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 GetAllUserSummaries():
 """Returns a string containing summary info for all GRR users."""

  grr_api = maintenance_utils.InitGRRRootAPI()
  user_wrappers = sorted(grr_api.ListGrrUsers(), key=lambda x: x.username)
  summaries = [_Summarize(w.data) for w in user_wrappers]
  return "\n\n".join(summaries)