I think the advantage of the allowance-based system is that it's a more credible measure, and there are more transparency issues with regard to the effectiveness; this is currently being discussed. It's more easily observed in emissions trading systems with absolute emissions counting.
There are a number of issues with transparency and accountability that are embedded in that versus the output-based pricing system. We have much more transparency on what the costs are and the regulatory burden associated with that. I think we have to be sensitive to those issues, as Ms. Swift was raising.