def _get_seqs_from_cluster(seqs, seen):
    """
    Returns the sequences that are already part of the cluster

    :param seqs: list of sequences ids
    :param clus_id: dict of sequences ids that are part of a cluster

    :returns:
        * :code:`already_in`list of cluster id that contained some of the sequences
        * :code:`not_in`list of sequences that don't belong to any cluster yet
    """
    already_in = set()
    not_in = []

    already_in = [e for e in map(seen.get, seqs)]
    # if isinstance(already_in, list):
    already_in = filter(None, already_in)
    not_in = set(seqs) - set(seen.keys())
    return list(set(already_in)), list(not_in)