def set_union(*sets):
    """Return the union of all the given sets.

    As of Python 2.6 you can write ``set.union(*sets)``.

    >>> from sympy.core.compatibility import set_union
    >>> set_union(set([1, 2]), set([2, 3]))
    set([1, 2, 3])
    >>> set_union()
    set()
    """
    rv = set()
    for s in sets:
        rv |= s
    return rv