Symmetric equilibrium existence and optimality in differentiated product markets
分析了一个三阶段博弈模型，证明在差异化产品市场中存在子博弈完美均衡，且均衡时产品对称分布、价格相同，同时发现社会福利最大化的产品多样性低于均衡水平。
Equilibrium existence and optimality are analysed in a market for products differentiated by their variety. A game of three stages is analysed. Firms enter in the first stage, choose varieties in the second stage, and choose prices in the third stage. The existence of subgame-perfect equilibria is established. At equilibrium products are symmetrically located in the space of characteristics and are offered at equal prices. The surplus maximizing solution is characterized, and it is shown that surplus maximizing product diversity is lower than the equilibrium one.