Characterizing C2 aggregate excess demand functions

We integrate and sharpen two characterizations of aggregate excess demand functions: we obtain Mas-Colell's (1977) equilibrium invariance, and strengthen Geanakoplos' (1984) weakly concave utility functions to strictly concave ones. Our proofs modify and extend Geanakoplos' utility construction. We note two applications: a sharper characterization of equilibrium price sets (cf Mas-Colell (1977)), and a basis for the studies of computable economies (Richter and Wong (1996)).