What is the difference between "aggregation" and a "representative agent?" I'm sorry if I'm not entirely clear on this question, but that's why I ask. It seems to me as if a representative agent is defined as a situation in which a competitive equilibrium can be reached by maximizing the utility of an object that can be interpreted as a "representative agent" whereas "aggregation" refers to a related situation where in competitive equilibrium prices don't depend on the distribution of an initial endowment. (Something to this effect.)
Could somebody clarify what these two concepts are and how they are related and/or different?