ions about when the market became sufficiently competitive to deregulate the activities of the formerly dominant player. Such a determina- tion is likely to be particularly difficult when technology and consumer demand are changing rapidly. The foregoing analysis underscores the extent to which regulators seeking to impose rate or access regulation must thread a very narrow needle even under the best of circumstances. Any such an intervention will only yield economic benefits if it forces prices closer to competitive levels. If the regulated price is set too high, the regulatory intervention will have no beneficial effect. If set too low, the intervention will deter investment while effectively forcing the incumbent network owner to cross subsidize providers of complementary services and new entrants. And any such intervention will be completely unnecessary to the extent that competitive entry into last-mile transmission is feasible. The alternative would be to allow the short-run supracompetitive returns to stimulate entry by alternative last-mile providers. By the standards imposed under modern competition policy, the availability of three (or perhaps four) last-mile options should be sufficient to dissipate any concerns about anticompetitive pricing in the last mile or vertical exclusion in complementary services. It is for this reason that courts and policy makers have been reluctant to compel access to a resource that is available from another source, even if it is only available at significant cost and in the relatively long Some scholars have asserted that because the dynamic efficiency gains will be compounded over time, they will necessarily exceed the short-run static efficiency losses. 37 This approach seems too simplistic. Whether the dynamic efficiency gains will dominate the static efficiency losses depends on the relative magnitude of the gains and losses, the speed of entry, and the appropriate discount rate. That said, a 36 See Iowa Utils. Bd., 525 U.S. at 388-9; Nat'l Cable & Telecomms. Ass'n V.