code: def external_answer(self, *sequences):
          
          # if this feature disabled
          if not getattr(self, 'external', False):
              return
          # all external libs doesn't support test_func
          if hasattr(self, 'test_func') and self.test_func is not self._ident:
              return
          # try to get external libs for algorithm
          libs = libraries.get_libs(self.__class__.__name__)
          for lib in libs:
              # if conditions not satisfied
              if not lib.check_conditions(self, *sequences):
                  continue
              # if library is not installed yet
              if not lib.get_function():
                  continue
  
              prepared_sequences = lib.prepare(*sequences)
              # fail side libraries silently and try next libs
              try:
                  return lib.func(*prepared_sequences)
              except Exception:
                  pass
docs: Try to get answer from known external libraries.