... agent.¹

If we think of an economy consisting of a population of agents each with their own observed vector of utilities $\epsilon$ and $f(\epsilon\vert X)$ is the density function representing the distribution of these ``types'' in the population, then $U(v_1,\ldots,v_D,X)$ represents the indirect or maximized utility of a typical person in the population. This is the reason U is referred to as a Social Surplus Function.

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