Axiomatization of the counting rule for cost-sharing with possibly redundant items

For cost allocation problems with an existing set of indivisible public resources with heterogeneous individual needs and non-rivalry access, an axiomatization is provided for the allocation rule that proportionally charges agents for a given resource with respect to their counting liability indices. The main result we obtain holds in the class of cost allocation rules that are additive in cost and simply combines a new independence property together with the well-known axioms of consistency and independence of supplementary items.