Exhaustible Resources, Non-Convex Costs and Contestability. A Reply
回应Geir Asheim的评论，承认原文脚注13的论证有误，并讨论可竞争市场中均衡需满足边际和平均套利条件，以及由此产生的混合租金（用户成本）与Hotelling原则的关系。
In his comment on my paper, Geir Asheim neatly disproves the arguments in my (1991) footnote 13 and the paragraph to which it refers. Trying to force the equilibrium into the mould of contestability, I was unmindful of the possibility that there could be a period when all firms produced. This possibility allows for Asheim's interesting observations, including that Ramsey prices result when price taking can be assumed if all firms are active. To begin I wish to stress the points which have been established in the two papers. First, equilibrium must satisfy two types of intertemporal arbitrage condition, a marginal and an average one. The novel condition is the latter, the contribution of contestability theory. Satisfying it leaves no incentive to reallocate a discrete amount of production to another time period. It helps give rise to what seems to be an unusual, hybrid sort of rent that Asheim identifies as the user cost: when contestability holds sway, it is price less average, not marginal, cost which rises at the rate of interest. Links to the more customary form of user cost, however, can be discerned in the marginal condition, which is necessary to preclude incentives to reallocate production at the margin among time periods. Newbery (1981) calls this Hotelling's arbitrage principle. It appears in Asheim's equation (2), since MR = P under his assumptions of first competition and then contestability.' On the downward-sloping part of AC, however, his equation