code: def is_nested(seq):
      """Returns true if its input is a nested structure.
  
      Refer to [tf.nest](https://www.tensorflow.org/api_docs/python/tf/nest)
      for the definition of a nested structure.
  
      Args:
        seq: the value to test.
  
      Returns:
        True if the input is a nested structure.
      """
      return nest_util.is_nested(nest_util.Modality.CORE, seq)
  
imports: from tensorflow.python.util import _pywrap_nest
  from tensorflow.python.util import _pywrap_utils
  from tensorflow.python.util import nest_util
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 6 for calling a global function with example usage: is_nested(seq) and returns: nest_util