  This paper studies whether a planner who only has information about the
network topology can discriminate among agents according to their network
position. The planner proposes a simple menu of contracts, one for each
location, in order to maximize total welfare, and agents choose among the menu.
This mechanism is immune to deviations by single agents, and to deviations by
groups of agents of sizes 2, 3 and 4 if side-payments are ruled out. However,
if compensations are allowed, groups of agents may have an incentive to jointly
deviate from the optimal contract in order to exploit other agents. We identify
network topologies for which the optimal contract is group incentive compatible
with transfers: undirected networks and regular oriented trees, and network
topologies for which the planner must assign uniform quantities: single root
and nested neighborhoods directed networks.
