def _set_count(sets, n, **kwargs):
    """return the elements which occur n times over the sequence of sets

    Parameters
    ----------
    sets : iterable of indexable objects
    n : int
        number of sets the element should occur in

    Returns
    -------
    indexable
        indexable with all elements that occured in n of the sets

    Notes
    -----
    used by both exclusive and intersection
    """
    sets = _set_preprocess(sets, **kwargs)
    i = as_index(_set_concatenate(sets), axis=0, base=True)
    # FIXME : this does not work for lex-keys
    return i.unique[i.count == n]