code: def _is_valid_einsum_equation(
      maybe_ab: str,
      maybe_bc: str,
      maybe_ac: str,
  ) -> bool:
      """Checks if three input strings form a valid einsum dense equation.
  
      Given three substrings `maybe_ab`, `maybe_bc`, and `maybe_ac`, this function
      checks if
      ```
      maybe_ab + ',' + maybe_bc + '->' + maybe_ac
      ```
      is an einsum equation of the form `ab,bc->ac`.
  
      Args:
        maybe_ab: The proposed `ab` substring.
        maybe_bc: The proposed `bc` substring.
        maybe_ac: The proposed `ac` substring.
  
      Returns:
        `True` if the three input strings form an einsum equation of the form
        `ab,bc->ac` and `False` otherwise.
      """
      a_substr = os.path.commonprefix([maybe_ab, maybe_ac])
      a_len = len(a_substr)
      b_substr = maybe_ab[a_len:]
      c_substr = maybe_ac[a_len:]
      return maybe_bc == b_substr + c_substr
  
file_path: privacy/tensorflow_privacy/privacy/fast_gradient_clipping/registry_functions/einsum_utils.py
imports: import enum
  import itertools
  import os
  import re
  from typing import Optional
  import tensorflow
  from tensorflow_privacy.privacy.fast_gradient_clipping import common_manip_utils
label_desc: Use image node_id 2 for calling a global function with example usage: _is_valid_einsum_equation(maybe_ab, maybe_bc, maybe_ac) and returns: unknown