Minimal-axiom characterizations of the Coleman and Banzhaf indices of voting power

Coleman [Coleman, J.S., 1971. Control of collectives and the power of a collectivity to act. In: Lieberman, B. (Ed.), Social Choice. Gordon and Breach, New York, pp. 269-298] suggested two indices of voting power, power to prevent an action and power to initiate an action. This paper develops two-axiom (and hence, minimal) characterizations of both the indices. We also show that similar characterizations can be done for other indices.