A common real-life problem is to fairly allocate a number of indivisible objects and a fixed amount of money among a group of agents. Fairness requires that each agent weakly prefers his consumption bundle to any other agent's bundle. In this context, fairness is incompatible with budget-balance...

In a voting model where the set of feasible alternatives is a subset of a product set $A = A_1\times\cdots\ldots{}A_m$ of $m$ finite categories, we characterize the set of all strategy-proof social choice functions for three different types of preference domains over $A$, namely for the domains...