def union(*sets, **kwargs):
    """all unique items which occur in any one of the sets

    Parameters
    ----------
    sets : tuple of indexable objects

    Returns
    -------
    union of all items in all sets
    """
    sets = _set_preprocess(sets, **kwargs)
    return as_index( _set_concatenate(sets), axis=0, base=True).unique
all unique items which occur in any one of the sets

    Parameters
    ----------
    sets : tuple of indexable objects

    Returns
    -------
    union of all items in all sets