Arrow's impossibility theorem was set out in his PhD thesis, Social choice and individual values. It shows the impossibility of designing rules for social decision making that obey all of a number of 'reasonable' criteria. It is often known as Arrow's paradox.
Working with Gerard Debreu[?] (who won the Nobel prize for this work in 1983), Arrow produced the first rigorous proof of the existence of a market clearing equilibrium, given certain restrictive assumptions. See general equilibrium.
... and the average family size is 3.51.
In the town the population is spread out with 29.5% under the age of 18, 6.7% from 18 to 24, 33.6% from 25 to 44, 20.6% from 45 to 64, ...