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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 list_registered_stateful_ops_without_inputs():
 """Returns set of registered stateful ops that do not expect inputs. This list is used to identify the ops to be included in the state-graph and that are subsequently fed into the apply-graphs. Returns: A set of strings. """

  return set([
      name
      for name, op in op_def_registry.get_registered_ops().items()
      if op.is_stateful and not op.input_arg
  ])