A good is nonrival if for any given level of production, the marginal cost of providing it to an additional consumer is 如果一种商品在生产的任意给定水平，向额外消费者提供商品的边际成本为零，那么不存在竞争。
A public good is provided efficiently when the vertical sum of the individual demands for the public good is equal to th当个人对公共商品需求的总和等于生产的边际成本时，公共商品的供给是最有效的。
Even if marginal gain of the newspaper firm which has certain market power in the advertisement market is equal to the m即使具备市场势力的报业厂商在广告市场的边际收益等于其在广告市场的边际成本，但是，不需要任何条件，报业厂商在发行市场的边际收益小于其在发行市场的边际成本；若具备一定条件，甚至连报业厂商的发行价格也小于其在发行市场的边际成本。
If the plane has empty seats, the cost of adding one more pa enger is minuscule, although the average cost of flying a p如果飞机有空的座位,每增加一个乘客成本就会更小,尽管每位飞行乘客的平均成本是500美元,边缘的价格仅仅是乘客将额外消费的花生和罐装汽水的价格.
If the plane has empty seats, the cost of adding one more passenger is minuscule, although the average cost of flying a 如果飞机有空的座位,每增加一个乘客成本就会更小,尽管每位飞行乘客的平均成本是500美元,边缘的价格仅仅是乘客将额外消费的花生和罐装汽水的价格.