CONVEX COMBINATIONS. Knowledge Problem is properly disgusted with advocates of one-size-fits-all command-and-control regulations who don't recognize a benefit.

Put another way, these folks don't want the utilities to be able to get a two-fer -- they do not want them to be able to reduce mercury in the process of pursuing other emission reductions. They want a separate mercury redution technology.

Don't serve such people a casserole. They want their meat separate from their potatoes. Alas, the notion of substitutability is not well understood by a lot of people, and it may not always be well taught by economists, including me.