r_index([0, 1, 2, 3, 0, 1, 2, 3], [0, 1]))
[]
>>> list(iter_index([[0, 1], [2, 3], [0, 1], [2, 3]], [0, 1]))
[0, 2]

See :func:`locate` for a more general means of finding the indexes
associated with particular values.

rì