def difference(actual, expected):
    """
    Returns strings describing the differences between actual and expected sets.

    Example::

        >>> difference({1, 2, 3}, {3, 4, 5})
        ('; added {1, 2}', '; removed {4, 5}')

        >>> difference({1}, {1})
        ('', '')

    :param set actual: the actual set
    :param set expected: the expected set
    """
    added = actual - expected
    if added:
        added = f'; added {added}'
    else:
        added = ''

    removed = expected - actual
    if removed:
        removed = f'; removed {removed}'
    else:
        removed = ''

    return added, removed