mr. keisler, you have a statute that does not have any language about no costs allowed. that also does not have what the american trucking association statute had are which was week public health only sufficient margin of safety. what you have is exactly what you said. you have a statute that focuses on causal contribution. right? so, this is a hard problem. right? because -- let me just sort of give you a a numerical example. let say that the standard is 100. and there's a state that has 120. and there are two states, x and y, that have each contributed 20. right? so, we only need 20 of those. we have 40. and the question is, how do you get from those 40 to those 20? the d.c. circuit would just say, we take ten from each. but if the question is only about contribution and that all the statute talks about there, has to be other ways we can make that determination of what contribution each should be legally responsible for. right? and what the epa said here was, we're going to distinguish between states that have put a lot of technology and a lot of money into this alread