def join_provenances(provenance1, provenance2):
    """
    Given two provenances (lists of id strings) join them together
    """
    # Use a dict to join them
    joined = dict(
        (p, True) for p in provenance1
    )
    joined.update(
        (p, True) for p in provenance2
    )
    return list(joined.keys())