code: def unify_walk(a, b, U):
      """
      OrV(list1) == OrV(list2) == OrV(intersection(list1, list2))
  
      """
      opt = a.options.intersection(b.options)
      if not opt:
          return False
      elif len(opt) == 1:
          v = BoundVariable("?", opt[0])
      else:
          v = OrVariable("?", opt)
      return U.merge(v, a, b)
  
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 9 for calling a global function with example usage: unify_walk(a, b, U) and returns: U, False