code: def unique_token_set(source_structure):
      """Checks that structured tokens are unique, and returns the set of values."""
      flat_tokens = nest.flatten(source_structure)
      flat_token_set = set(flat_tokens)
      if len(flat_tokens) != len(flat_token_set):
          raise ValueError(
              "Restructure tokens must be unique. Saw: {}".format(
                  source_structure
              )
          )
      return flat_token_set
  
imports: import six
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import bijector
  from tensorflow_probability.python.bijectors import invert
  from tensorflow_probability.python.internal import dtype_util
  from tensorflow_probability.python.internal import nest_util
  from tensorflow_probability.python.internal import parameter_properties
  from tensorflow.python.util import nest
label_desc: Use image node_id 1 for calling a global function with example usage: unique_token_set(source_structure) and returns: flat_token_set