code: def ordered_union(l1, l2):
    
    out = []
    for e in l1 + l2:
      if e not in out:
        out.append(e)
    return out
docs: Return the union of l1 and l2, with a deterministic ordering.
    (Union of python sets does not necessarily have a consisten iteration
    order)
    :param l1: list of items
    :param l2: list of items
    :returns: list containing one copy of each item that is in l1 or in l2