minutes for a bottle this court should reverse and remand because the district court erred in ignoring a longstanding treasury department regulation addressing whether certain truck components are subject to the  because the statute did not in chevron parlance address the precise question it is to whether components installed on a truck chassis or body that if that do not contribute to the highway transportation function of the truck council just before we get to step two i want to figure out why we don't stop at step one and i think your answer may be the mayo case but i want to at least challenge you a little bit on this particular case which is under any reasonable definition of the word part this diesel particular not the one we should look to there may be a question that the statute is posed that this doctor doesn't directly addressing and here we have the unusual situation where you have a heart that in the entire history of trucks has never been wrote and are just going to follow up maybe it's different and mayo's involve the word student and the problem i have is mayo was in pay us as applied to that particular case a student could be somebody who spends one hundred percent of their time in class a full time student or student can be somebody like this where you don't spend one hundred percent of your time in class so you're actually doing something part of your course of study that requires like an extra chip on enter chip to get paid for doing something and so the definition of student even though we kind of know what it means was ambiguous in that sense and so under chevron step one it was reasonable to go on to chevron step two i guess i'm not sure why it's reasonable to there is chevron step two here because again i don't of any other definition of the word part that doesn't include this piece or particular filter whether it be a definition a technical definition or otherwise maybe you can help me come up with a different definition i think under mayo there w place for decades the regulation we relied on has been in place for forty years there have been the parts and accessories definition are in place for decades and to then look at the statute and say oh everything that sold with the truck ma under the stock to be taxable just flies in the face of an entire regulatory regime that it been in place when when congress enacted forty fifty one so we do believe that the district court's decision was and the district court did not even address the argument at all in a in a footnote that what you ordered so i in the opposition to the motion to dismiss that the government filed thompson truck relied on the because the case was decided on a motion to dismiss there wasn't you know a full development of the factual record and the court never even reached whether the regulation would apply well the reason why i'm asking is because this would seem like a part under the plain language statute then you get to the regulation you're like wow is this really a machine is this really a quick minute i mean then you look at the plain language of those particular provisions and you're like i don't know if it really fits in those things so i'm not even sure that the regulation applies and filters serves is to me this air quality you know regulatory requirement that otherwise no one would ever have it on a truck it doesn't increase the trucks fuel efficiency it doesn't increase its ability to operate efficiently  describes a category of types of of equipment machinery equipment that does contribute to the highway transportation function and it talks about loading or unloading a quick moment towing winches and all other machinery or  quitman contributing to are the maintenance or safety of the vehicle the preservation of cargo or the comfort and convenience of the passengers so you can argue that it would fall within that category plus a muffler is his that's entirely sort of separate from the normal operation of functionality of the truck can and can they run the truck on a highway without the diesel particulate thompson truck do you really know i mean functional highway transportation function remember the brake elation doesn't say common truck functions or something of that nature but doesn't it contribute to the highway transportation function because the truck can't run on the highway without it i think it depends on how you define and function so we would interpret the regulation to use function to mean how the truck operates as a truck rather than meeting some journal  is this a highway vehicle is it being used for a highway transportation function and so that regulation was was clarifying that there are certain kinds of components in equipment that are installed on the truck that were just just because  as long as it came up and seems to be in the court's mind as a judge just discussed the mayor case talked about students but students in that case were people who wore two hats they had two different functions so that's where the ambiguity ambiguity came from are they employees well yes they are they students yes they are a decent particularly filter is nothing but a truck park it was designed for th it functions as a truck part and can't function anywhere else it can't be taken off the truck and used for any other purpose it can't do any other thing other than be a part of the exhaust system of the trucks and function as a component to make the trucks able to go on the highways that's the distinction with mayo in my mind the students were had different purposes that the p f does not the fact that roads it can't even move off the parking lot without the filter installed the practical matter is part of it absolutely absolutely and i want to get into what it's not the way the cour case was decided but i want to get into the how highway transportation function before you get there though you know i think judge arnold made an excellent point which is you know if it's so plain if part is so plain then why have th regulatory history where over the course of time the regulations define the word part in a way that provides additional explanation what what do you have your spawn of that argument well in part  complicated to respond to and complicated to look into because there were all these iterations and definitions and they seemed to broaden the language of part at the time the regulations in designed to be a test they were expanding the definition of part not limiting it in any way and now congress has changed the statute and the new regulation that goes along with this statute does not have these regulations in place these definitions in place as though again as you say the definition of part is pretty well established we really don't need a regulation at this  time to define what that is it's pretty self evident so i believe that congress's as judge arnold was saying congress's intent is clear and the history is clear and further regular ation isn't necessary now i understand well there's a new regulation in place one forty five point four zero five one which was designed to go along with this new statute forty fifty one the old statue was forty sixty one and that and the new yes yes exactly where it was charged against the first retail sale as opposed to charging the manufacturer and the new regulations that go along with the new statute do not have the part definition do not include the old definition of part therefore that's why the district court was left with the statutory language the definition or the dictionary definition of what a part is and that functions just fine that makes it clear the word part is at this point is is very clear it's a basic component of the machine it issued here it it not an option that you purchased years later it's not an aftermarket equipment piece that you install later on it's very basic it's sold at the first retail sale and if  purchaser came to you and bought the truck and this filter wasn't on it he would come back and complain and say i didn't get the complete truck that i purchased i can't use this truck without this filter that's that's a part that's a basic component of this truck and that's why our two arguments are really an argument was that in our brief was that it can be separated out it is separated out as a part in one way but it's also inseparable from the basic unit of taxation here which is the truck where do you stop taking off parts to determine what is a part what's a truck that you bought at the first retail sell you bought all the parts that were on the truck at the time of the retail sale they are the parts of the truck and therefore i think we think that the filter is taxable simply under the part under the word tractor is it as it is in the statute tractor for use on highway pulling trailers trailers but it also is included in the term part which is a separate definition which by the way it's a separate term they included because they didn't want somebody buying a truck and then separately say through amazon buying an exhaust system and then through amazon buying a steering wheel and that way trying to avoid the excise tax the idea is no you buy those things later in their component parts of the truck that you need to run the truck their parts their taxable the subject to the tax in the event with regard to the highway transfer the new regulation which i believe the i r s refers to as the installed equipment regulation which the appellant relies on and says that if it's not needed for highway transportation function it's not a part that's taxed first of all that's not the language that's not the way the statute this regulation reads what it really the way it reads  regardless of whether separate sales of the machinery or quit would be subject to tax on automated parts or accessories imposed under the statute well then you look at this regulation in other words regardless of  when you're done the dirt terminations of party or equipment or accessory first and regardless of how you come down there this regulation says if it aids the transportation function of the truck it's going to be taxed to they're for you don't get to this regulation at all if you've already decided that something is taxed as a part so that's one reason that this this regulation simply doesn't apply in addition to the fact that the plain language of the statute covers what part of this and this the statute this regulation doesn't kick in until it's not taxed as a part doesn't order examples in the regulations about what counts is something that contributes to the highway transportation function of the vehicle and what doesn't all they are and how do you do what do you think the dividing line is between those the ones that are and the ones that are not i mean how would you define what it is the regulators getting at yes what i what i believe the regulator is getting at is does the part equipment thing in in question aid the transportation function of the vehicle in other words if you're building a truck to carry loves then the parts on the sides that hold the logs make sure they don't fall off that that contributes to the highway transportation function the truck can't do the job it's designed to do and those things aren't the load the truck is carrying so are saying i don't put words in your mouth what is it  because they cannot do the transportation function that they need to do with these trucks without that filter and start i would also call this court's attention to a technical advice memorandum the i r s issued in two thousand and one we didn't mention this in our brief because we don't think the regulation applies and we didn't get deeply into the highway transportation function but this is found at two thousand two westlaw two eight seven seven eight it's a technical advice memorandum that discusses for several pages what is the difference between something that contributes to the highway transportation function and what is something that does not contribute to the highway transportation function and in particular this technical advice memorandum talks about something that  compaction equipment and top doors of refuse collection vehicles and one of the things it says is that we're guard to the compaction equipment that compresses refuse in a trash truck it also enables the vehicle to carry more than it would be able to carry without the compaction therefore it as to the utility of the vehicle and transporting a load over the highways in other words it doesn't have to be just the part that makes go it's not tied with the propulsion or the drive the physical movement of the vehicle it's tied with the function of the vehicle and doesn't allow it to do what it needs to do is not tied up with the mechanics of making an engine go or making the tires go around that's it's tied up with the transportation function as opposed to the physical moving function and that's why this filter is absolutely a part of the truck even if you look at these regulations because without it there would be no highway transportation function well i can do it  could operate illegally yes or yes you could or i mean i think there could be yes but presumably the company does not want to do that i agree with that but it's not a practical impediment  that's just really a self cleaning mechanism it's not as though again you can take the d b f off of the truck and use it as some sort of regenerate or somewhere on a farm or even in someone's backyard or in a warehouse it's regenerating because the cert builds up in the filter and that cleans cleans the filter out and if you don't do that the truck will either shut down because it's all clogged or it will you will have to take it into a dealer or somebody and have that cleaned out for you and that's an expense that you don't want to incur say every i don't know how many thousand miles it require but you want that fixed function to be done in the filters the truck is going  cleaning itself and doing that for you plus that's the purpose of the filter is to blow away to burn away the pollution that is being collected that's part of the pollution reduction function of the of the d p f so that is not a separate function that that should be considered in short i would just like to end with the fact that a statement that this case was come correctly decided and that is the standard under it paul and twamley the court has no questions i'll be seated thank you very much what things sold with the particular tractor or truck issue should be subject to tax so the agency has has long adopted an interpretation of the statute that's very different from what the district court did here which was to say that everything that sold with the truck is taxable statutory scheme where if you had a party or accessory that was not sold at the time the truck was sold it would be subject to tax unless it was the part of excess through that was used with automobiles so that's what that language is referring to the government is interpret ing the installed equipment regulation to say that even if a part of accessory wouldn't be taxable under the statute it becomes taxable into this regulation and that's just not how regulations w regulation wouldn't impose a tax at that statute didn't impose and i think one way to look at this is that for many decades the parts and accessories regulatory definition was operating side by side with the installed equipment regulatory