code: def unflatten1(flat_list, reverse_list):
      
      unflat_list2 = [[flat_list[index] for index in tup]
                      for tup in reverse_list]
      return unflat_list2
docs: Rebuilds unflat list from invertible_flatten1
  
      Args:
          flat_list (list): the flattened list
          reverse_list (list): the list which undoes flattenting
  
      Returns:
          unflat_list2: original nested list
  
  
      SeeAlso:
          invertible_flatten1
          invertible_flatten2
          unflatten2