code: def _index_to_einsum_variable(i):
      """Coverts an index to a einsum variable name.
  
      We simply map indices to lowercase characters, e.g. 0 -> 'a', 1 -> 'b'.
      """
      return string.ascii_lowercase[i]
  
imports: import collections
  import math
  import string
  import numpy
  from keras import constraints
  from keras import initializers
  from keras import ops
  from keras import regularizers
  from keras.api_export import keras_export
  from keras.layers.activations.softmax import Softmax
  from keras.layers.core.einsum_dense import EinsumDense
  from keras.layers.layer import Layer
  from keras.layers.regularization.dropout import Dropout
label_desc: Use image node_id 1 for calling a global function with example usage: _index_to_einsum_variable(i) and returns: string