code: def unify_walk(l1, l2, U):
      """
      Tries to unify each corresponding pair of elements from l1 and l2.
  
      """
      if len(l1) != len(l2):
          return False
      for x1, x2 in zip(l1, l2):
          U = unify_walk(x1, x2, U)
          if U is False:
              return False
      return U
  
imports: from __future__ import absolute_import, print_function, division
  from copy import copy
  from functools import partial
  from theano.gof.utils import ANY_TYPE, comm_guard, FALL_THROUGH, iteritems
label_desc: Use image node_id 13 for calling a global function with example usage: unify_walk(l1, l2, U) and returns: U, False, False