def generate_path(start, ref, nonref, stop):
    """

    Given source, sink, and ref/non-ref nodes enumerate all possible paths

    """
    ref_path = [x for x in [start, ref, stop] if x != "0"]
    nonref_path = [x for x in [start, nonref, stop] if x != "0"]
    return [ref_path, nonref_path]