Search at the Margin
将搜索理论扩展到多不可分单位和完全可分资产，分别用归纳法和递归法求解。模型适用于价格数量讨价还价，发现买方议价能力增强等同于搜索摩擦增大。
We extend search theory to multiple indivisible units and perfectly divisible assets, solving them respectively with induction and recursion. Buyer demands and prices are random, and the seller can partially exercise orders. With divisible assets, the Bellman value function is increasing and strictly concave, and the optimal reservation price falls in the position, reflecting increasing holding costs (opportunity cost of delaying optionality for inframarginal units). The marginal value exists, and is strictly convex with a falling purchase cap density. Our model is amenable to price-quantity bargaining; e.g., greater buyer bargaining power is tantamount to greater search frictions.