罗莫的高宏第五章有这么一段话
Because markets are competitive, externalities are absent, and there are a
finite number of individuals, the model’s equilibrium must correspond to
the Pareto optimum. Because of this, we can find the equilibrium either
by ignoring markets and finding the social optimum directly, or by solving
for the competitive equilibrium.

哪位前辈能解释一下为什么均衡必须是帕累托均衡？后面的两种解决方法，一个是社会最优（ social optimum ），一个是竞争性均衡（competitive equilibrium），什么关系？