def Nor(*xs, simplify=True):
    """Expression NOR (not OR) operator

    If *simplify* is ``True``, return a simplified expression.
    """
    xs = [Expression.box(x).node for x in xs]
    y = exprnode.not_(exprnode.or_(*xs))
    if simplify:
        y = y.simplify()
    return _expr(y)