R1, = 1, L, such that total costs were covered: There are three problems with this approach. First, due to economies of scope in the provision of network services, each R1 would necessarily equal or exceed the incremental cost of the UNE service, with at least one strictly exceeding the UNE service's incremental cost. It would certainly not be advisable or economically correct to have any attributed cost below any of the UNE service's incremental costs. Thus, the question is how to allocate the joint and common costs of the UNE services. This problem arises even if there are no final network services. This is the classic problem of allocation of joint and common costs by regulators. All administrative approaches to this problem are necessarily arbitrary, as noted earlier, no matter what are the types of services, and UNE services are no exception. Second, there are costs that are attributable to final services, that is, the long-run incremental costs of each of those services. Assigning all shares of total costs to the services of elements presents a distorted picture of total costs or at least a distorted picture of the sources of costs, the final services and UNE services. If final services are then to be sold, the UNE incremental costs will not provide much of a guide to assigning costs to final services. Finally, the same problem of short-run versus long-run incremental cost arises. If total costs are to be divided among elements on the basis of long-run incremental costs, but some inputs to the network are fixed, there will be a shortfall relative to short-run incremental costs: Therefore, with fixed inputs in an existing network, short-run incremental cost may be a better guide to the attributable costs of network services. Some share of total short-run costs can be assigned to network elements to reflect the joint and common costs that are shared with final services, with the caveat that such adminis- trative allocations are arbitrary. As later discussion shows, relative prices established by markets provi