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Abstract:
We study the problem of designing group-strategyproof cost-sharing mechanisms.
The players report their bids for getting serviced and the mechanism decides a
set of players that are going to be serviced and how much each one of them is
going to pay. We determine three conditions: Fence Monotonicity, Stability of
the allocation and Validity of the tie-breaking rule that are necessary and
sufficient for group-strategyproofness, regardless of the cost function.
Consequently, Fence Monotonicity characterizes group-strategyproof cost-sharing
schemes closing an important open problem. Finally, we use our results to prove
that there exist families of cost functions, where any group-strategyproof
mechanism has arbitrarily poor budget balance.