def find_last_to_last(lis, elem_set) -> int:
    """Returns the index of last to last occurance of any element of elem_set in lis,
    if element is not found at least twice, returns -1."""
    count = 0
    for idx, elem2 in reversed(list(enumerate(lis))):
        if elem2 in elem_set:
            count += 1
        if count == 2:
            return idx
    return 0