Ring & Pinion v. ARB: No Foreseeability Limitation on DOE

Ring & Pinion Service Inc. v. ARB Corporation Ltd. (Fed. Cir. 2014) Opinion
Panel: Moore (author), Clevenger, Reyna

One of the main justifications for the doctrine of equivalents is that it prevents patents from becoming worthless as a result of unforeseeable changes in technology.  As Judge Rader observed in his concurrence in Festo:

A primary justification for the doctrine of equivalents is to accommodate after-arising technology. Without a doctrine of equivalents, any claim drafted in current technological terms could be easily circumvented after the advent of an advance in technology. A claim using the terms “anode” and “cathode” from tube technology would lack the “collectors” and “emitters” of transistor technology that emerged in 1948. Thus, without a doctrine of equivalents, infringers in 1949 would have unfettered license to appropriate all patented technology using the out-dated terms “cathode” and “anode”. 

This case deals with the inverse: whether the doctrine of equivalents can apply when a technology was foreseeable at the time of patenting.

R&P sought a declaratory judgment that its product did not infringe ARB’s patent.  The parties agreed that R&P’s product literally met all of the limitations of claim 1 of the patent except for one, which they agreed was present as an equivalent in R&P’s product.  However, they disagreed over whether the doctrine of equivalents could apply since the equivalent would have been foreseeable to a person having ordinary skill in the art at the time the application was filed.  The parties thus stipulated that infringement in this case turned on the legal question of whether “foreseeability of an equivalent at the time of application prevents use of the doctrine of equivalents.”  The district court ruled that foreseeability did not preclude application of the doctrine of equivalents, but granted summary judgment to R&P on a vitiation theory.

On appeal, the Federal Circuit agreed with the district court that forseeability is not a limitation on the DOE:

There is not, nor has there ever been, a foreseeability limitation on the application of the doctrine of equivalents. It has long been clear that known interchangeability weighs in favor of finding infringement under the doctrine of equivalents.  [the CAFC cites a number of cases discussing interchangeability, including Warner-Jenkinson and Graver Tank]. Excluding equivalents that were foreseeable at the time of patenting would directly conflict with these holdings that “known interchangeability” supports infringement under the doctrine of equivalents. We conclude that the foreseeability of an equivalent at the time of patenting is not a bar to a finding of infringement under the doctrine of equivalents.

Slip Op. at 4-5.

Nor did it matter that the claim element involved was drafted in means-plus-function terms.  The doctrine of equivalents applies equally to these types of claim terms, and there is no “partial” foreseeability limitation here.  “Nothing in Chiuminatta or in any other case cited by R&P supports its assertion that there exists a foreseeability exception to the doctrine of equivalents that applies to means-plus-function or any other claim terms.”  Slip Op. at 7.

The defendant here thus lost on infringement because there is no foreseeability limitation on the use of the doctrine of equivalents.  Furthermore, the stipulation that the parties entered into precluded consideration of other potential issues: the district court erred by not enforcing that stipulation.

Policy rationale: Given that a primary rationale for the doctrine of equivalents is to address the problem of after-arising technology, what is the basis for concluding that the DOE also extends to foreseeable technologies, i.e.: those that the patent drafter could have included in the patent.  While Ring & Pinion v. ARB does not offer an explanation, the Supreme Court’s opinion in Festo does:

“The language in the patent claims may not capture every nuance of the invention or describe with complete precision the range of its novelty. If patents were always interpreted by their literal terms, their value would be greatly diminished. Unimportant and insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. For this reason, the clearest rule of patent interpretation, literalism, may conserve judicial resources but is not necessarily the most efficient rule. The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described.”
Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 535 U.S. 722, 731-32 (2002).

In other words, patent drafters are not omniscient; they are human beings who are using an imperfect tool (language) to describe an intangible concept.  In addition, patent drafters are only one person or a few people, whereas competitors seeking to design around the patent may be numerous (the game show 1 vs. 100 was premised on a concept like this).  Under this view, the doctrine of equivalents tries to level the playing field.

Furthermore, although not discussed by the court, foreseeability remains an important component of the prosecution history estoppel analysis.  Under Festo, the presumption arising from a narrowing amendment can be rebutted if the patentee can show that the equivalent was unforeseeable at the time of amendment.  535 U.S. at 741.  But Ring & Pinion did not assert that there was a narrowing amendment, so this application of foreseeability was irrelevant.

 

 

37 thoughts on “Ring & Pinion v. ARB: No Foreseeability Limitation on DOE

  1. 7

    It is not surprising that my new friend Random is missing on a DOE thread.

    Maybe he is out still looking for applications (and case law requiring) actual specific code.

    While I have no doubt he may find applications with code, he will not find case law demanding such.

    And for very good reason.

    A phrase from this case comes to mind. Let’s let Random chew on it: “The doctrine of equivalents covers accused structures that perform substantially the same function in substantially the same way with substantially the same results.

    1. 7.1

      I’m right here darling. How unfortunate you don’t see this proves me right, as this is the way it ought to be done.

      “Nor did it matter that the claim element involved was drafted in means-plus-function terms. The doctrine of equivalents applies equally to these types of claim terms, and there is no “partial” foreseeability limitation here. “Nothing in Chiuminatta or in any other case cited by R&P supports its assertion that there exists a foreseeability exception to the doctrine of equivalents that applies to means-plus-function or any other claim terms.” Slip Op. at 7.”

      That is actually the proper way to do it. Draft the software claim in limitations that are algorithm steps using means-plus, and then with respect to a given infringer the court will decide if the steps taken by the infringer are equivalent steps to the steps taken by the patentee.

      Incorrect way of doing it: Attempting to avoid the question of equivalence with impermissibly broad functional claiming up front, thereby making it a question of literal infringement to a much broader scope. (Note also that this would apply DOE to the straight functional limitation as well, essentially allowing an applicant to double dip on equivalency.)

      I hope you understand the procedural and substantive differences between the two methods, but I suspect you’re too dumb. As I have said before, I have zero problems with disclosing your particular algorithm and then claiming it in 112, 6th. That is a substantially different scope from disclosing your algorithm and then claiming every algorithm which has the same result by using non-means functional language.

    2. 7.2

      Also I should add: “A phrase from this case comes to mind. Let’s let Random chew on it: “The doctrine of equivalents covers accused structures that perform substantially the same function in substantially the same way with substantially the same results.“

      Yeah, most definitely. Too bad a claim to a full functional scope when the applicant is only in possession of a single means covers all structures “that perform substantially the same function”. Missing are the other two requirements: substantially the same way with substantially the same results. Just another reason why the proper scope of a software claim is the particular disclosed algorithm, not the function.

    3. 7.3

      PS – Does it hurt when you gleefully quote language from a case that we’re both in total agreement with and it highlights why my interpretation of the larger issue is correct while yours is wrong?

      1. 7.3.1

        LOL – does it hurt? Why should it hurt when it shows I am right? Oh wait, you are spin that strawman thing again…. (What you claim is missing is not – it is merely not there at an actual code level which was your pathetic argument)

        Try climbing up a rung or two on the ladder of abstraction Pumpkin.

        Or at least substantially so.

      2. 7.3.2

        …and note too that DOE was applied to BOTH means plus and none means plus….

        But keep on declaring your ‘victory’ otherwise – it’s a nice delusional trait you share with Malcolm.

        1. 7.3.2.1

          “(What you claim is missing is not – it is merely not there at an actual code level which was your pathetic argument)”

          Yep, I was right, you’re too dumb. I’ll use simple ideas so you can understand:

          Situation 1 – Kyle invents code which does steps A, B, C to achieve function D. Kyle claims A, B, C in means plus along with other limitations. The PTO considers if A, B and C are enabled and if Kyle possesses them. PTO concludes the tests are met and Kyle is granted a patent. Lizzy comes along advertising her machine that achieves D using steps E, F. Kyle sues Lizzy.

          The court places the burden on Kyle to show that E and F are equivalent to A, B, C. Any attack on the validity of the claim with A, B, C is held to a higher standard as they are presumed valid, but that’s largely irrelevant to Lizzy. Notably, however, E, F, requires one less step, which may make it a substantially different manner, as the elimination of a step while maintaining functionality is a basis for finding non-obviousness. Kyle likely loses this case.

          Further, Matt comes along and achieves D using clearly different steps W,X,Y,Z. Kyle can’t sue Matt.

          Compare that with Situation 2 – Kyle invents code which does steps A, B, C to achieve function D. Kyle claims any machine doing function D, along with other limitations. The PTO considers if Kyle has enabled and is in possession of the full range of D. Because the PTO has unfortunately hired anon, it concludes the tests are met and Kyle is granted a patent. Lizzy comes along advertising her machine that achieves D using steps E, F. Kyle sues Lizzy.

          The only burden the court places on Kyle is to prove what Lizzy has admitted in her advertising – that Lizzy sells a machine that achieves D. Any attack on the validity of the claim involving D is held to a higher standard as it is presumed valid, and an attack on D’s validity is the only real means of defense. Kyle likely wins this case.

          Further, Matt comes along and achieves D using clearly different steps W,X,Y,Z. Kyle sues Matt and wins.

          And why is A,B,C in means the proper way of claiming it? Exactly because there is zero proof on the record, or within legal reasoning, that Kyle ever possessed E,F or W,X,Y,Z, and that is the standard.

          anon has yet to provide a case where a claim to a new functionality has withstood a written description challenge, and last I checked, written description was a requirement that had to be met.

          NWPA, on the other hand, apparently can’t read statutes since he refuses to admit that written description is a requirement at all. Either that or his fails to understand that the standard is not whether one of ordinary skill in the art could invent E,F or W,X,Y,Z, (the scope of enablement, as he loves to state the test as) the question is whether Kyle specifically had possession of them. There is nothing on the record at all that Kyle ever considered E,F or W,X,Y,Z or that they would achieve the function as well.

          anon at least admits that WD is a requirement, he just spouts “ladders of abstraction”, forgetting that as the scope changes (by moving up the ladder of abstraction) the burden on the applicant increases, as he must now prove possession of the broader scope. It’s unclear if anon thinks the original single means also fills the larger scope which is just an incorrect assessment of the law (one wonders why Morse would be denied his claim under this scope), or if it can be done by simply using the words of the broader scope (which would allow one to claim “all solutions to the problem”, which, if so, would remove the need for a having a doctrine of equivalents altogether).

          “and note too that DOE was applied to BOTH means plus and none means plus”

          Yes…I don’t see the point you’re trying to make? Of course DOE is applied to both. What does that have to do with anything? The question is if applicant shows he does X, must he claim X and then argue in court that Y is similar (as was done here), or is he allowed to show X, claim X+Y and then argue literal infringement on Y? Note also that applying DOE to X+Y would allow the applicant to reach Z. The latter proposition (which is what you seek to reach with your expanded, non-means-plus functional scope) shifts both the procedure and the substantive burden around on Y and would allow the applicant to double-dip off of similarity to reach Z.

          1. 7.3.2.1.1

            That’s a lot of nonsense and dust-kicking that simply does not prove your point Random.

            Nice strawman as to ‘moving burdens’ with going up the ladder of abstraction. Unfortunately for you – your point had been that you needed actual code; that is, that you had to have the bottom rung. Clearly you do not. Clearly a rung above that shows possession of A,B,C Even if only providing a description and not code for A,B,C suffices for both A,B,C and ANY alphabet you want to vomit out that meets the tri-fold substantiality test – which has been my point.

            Clearly you are wrong in your rants. It’s rather sad that you have such a hard time admitting that I am right. Don’t worry, others like Malcolm, 6, Ned and Leopold also have this affliction.

            Hmmm, with that note, maybe you should worry.

            1. 7.3.2.1.1.1

              I never said you needed actual code. I have always said that the standard is laid out in Aristocrat, where they stated code or algorithm. In Aristocrat they make very clear that algorithm requires just that – steps, not a statement that you achieve the function and that is it.

              It’s a very simple rule, if I claim function D, there better be a Fig with a handful of boxes that begin with “Start D” and ends with “End D”, or a similar disclosure. Then, if the Examiner can show that D can be achieved in ways other than the boxes (for example, via E,F), you haven’t achieved the full scope of D, you can’t claim D, and what you’re entitled to claim is the boxes (your particular algorithm), as that is the only thing you have proved you have.

              What can’t be done, and what you see all the time is a Fig that has the following boxes:

              -Turn computer on
              -Put computer into environment where problem arises
              -Determine problem arises
              -Use new function D to solve problem
              -Profit

              Applicant then claims in his limitations “Do function D”. That’s no description of D at all. In this situation the applicant isn’t entitled to anything.

              “that is, that you had to have the bottom rung.”

              For a new function, you have to have the bottom rung, but the bottom rung is not actual code. Again, see Aristocrat, the bottom rung is the algorithm steps. They outright say in Aristocrat “we have never required the actual code”.

              “Clearly a rung above that shows possession of A,B,C Even if only providing a description and not code for A,B,C suffices for both A,B,C and ANY alphabet you want to vomit out that meets the tri-fold substantiality test – which has been my point.”

              Moving up a rung is inductive. If you show A, B, C you have described A, B, C.

              If A, B, C cause D, describing A, B, C does not describe the full scope of D and fails for 112, 1st.

              Moreover, saying only that “I have D” (without disclosing ABC or other means) does not prove you have D, nor A, B, C, and consequently the applicant is entitled to nothing.

              The only valid way to claim D – Applicant must prove he is in possession of every algorithm which causes D, which as a practical matter is impossible.

              This case, which for some reason you thought proves your point, actually proves mine, because “as a practical matter is impossible” seems scary until you note that by simply disclosing and claiming A, B and C, the court will give you a larger scope than them under DOE. Not “all of D” scope, but still a much larger scope. What is improper is you trying to force the court to take it beforehand, by yourself, by claiming D to begin with. You don’t possess D, any more than Morse owned every machine that performed a function of printing letters at a distance. Morse owned HIS telegraph, and his and similar telegraphs are protected under DOE. But “printing letters at a distance” reads on a networked computer, and if the claim had been allowed to stand he could sue on any networked computer (assuming his patent had a life that long) under your theory. Under mine, he couldn’t. That’s a substantial difference in scope, especially in computer software where a decade may act like a century

          2. 7.3.2.1.2

            Random, do people actually file for and receive patents on “computer programmed to achieve function X?”

            I’ve never seen it, nor have I have every tried for such a claim.

            1. 7.3.2.1.2.1

              People routinely file and are granted patents on what I said in response to anon, it largely goes like this:

              -A processor
              -Limitations that are necessary to define the operating environment in which a problem crops up
              -A non-means-plus limitation reciting a function which solves the problem

              It’s clear the operating environment limitations are old, so the question becomes “Is applicant claiming applying an old function to an old environment in a novel and non-obvious way, or is he claiming a new function to solve the problem?”

              The former is generally not a problem, as KSR would function to render obvious old function + old environment and the office is very good at making 103 rejections.

              The latter, however, is very common, and represents an overreach of what the applicant has invented. Once you know a novel function is what is being dealt with, the specification is checked to determine what the teaching for the new function is. In, I would say maybe a third of the cases, the teaching is literally “The computer does function D” or similar language. In other words, the specification purports to describe the function by restating the claim language in a single sentence. That’s what the spec says, I do function D, as if 112, 1st is met by simply stating something. These applications are, under the law, entitled to nothing. They should never issue, because the applicant simply hasn’t taught the public or described anything. They have failed to describe D, adding a description of D would be new matter, and they have no smaller scope which they can fall back upon.

              In 90% of the remaining cases, applicant does describe a single set of method steps, ABC, which achieve the function D. In this case, we have a scope problem. The applicant has described and enabled ABC, but ABC is not the sum scope of D. These claims issue constantly, partially because cases like Lizardtech are few and far between and the signal gets lost in the noise, and partially because the office has multiple internal reasons that cause them to issue.

              So to answer your question, nobody files for a patent on a computer to achieve function X, but the other limitations are the only time that X would be used and X is so broad as to foreclose any designing around X.

            2. 7.3.2.1.2.2

              Got it.

              CLEARLY, functional at the point of novelty and indefinite per Halliburton.

              As to the internal problems at the PTO that allow such claims … well I would like to here more. Hopefully, Obama’s new push on functional claiming will help.

              Hopefully, so will the Supreme Court in Nautilus v. Biosig, particularly if they reaffirm Halliburton in spades.

            3. 7.3.2.1.2.3

              Ned repeats his well-worn canardss and errors: “CLEARLY, functional at the point of novelty and indefinite per Halliburton.

              PON is a canard.
              Halliburton has been abrogated.

            4. 7.3.2.1.2.4

              X is so broad as to foreclose any designing around X

              Utter nonsense. X is X and only X. Y is not X. If one designs around by using Y instead of X you have no issue whatsoever.

              Any patent for ANYTHING Z is as broad as Z and that is it.

              You are making the child mistake of confusing breadth for indefiniteness.

              The rest is you attempting to kick up dust.

            5. 7.3.2.1.2.5

              “As to the internal problems at the PTO that allow such claims … well I would like to here more. Hopefully, Obama’s new push on functional claiming will help.”

              I guess they’re not problems so much as a combination of things which may or may not be in the PTO’s control. If you’re going to start people at $67k in one of the highest cost of living places in the US, and a place where there happen to be a lot of private firms which do the same kind of work all around, you’re not going to attract a lot of people with law school debt. It’s mostly engineers who get hired (as engineering is a requirement of the job). It should be no surprise that while all patent law involves questions of engineering and questions of law, its clear that the office is much better at the questions tipping toward the engineering side surrounding 102/103 than the legal ones surrounding 101 and 112, 1st.

              Matching an engineer with under three months of legal training against someone who went to law school for years, probably took patent or IP courses, and had to pass a certification test doesn’t make for a fair fight in arguments over legal issues, so the viewpoint of most examiners is that it’s not worth it. I will say that this begins to disappear as each respective party becomes more skilled (an examiner handles many more cases in the same time frame and catches up somewhat on the legal knowledge) but people on the private side tend to be doing this as their career while examiners have high turnover. The office also used to pay in to send people to law school, it no longer does. There are also limitations on how quickly you can be promoted and it is questionable whether promotion is something in your financial interest anyway, both of which incentivize those best at the job to find employment elsewhere.

              Then there are internal means of quality checks to which I will only say this: It would stand to reason from anyone who looks in on a top-down structure that the more involved a question is with the particulars of a task that is delegated to a subordinate, the harder it is for their supervisor to notice a failure and punish for it. One need understand only the basics of stick-and-carrot motivation (or perhaps watch Officespace) to understand why some actions which should be undertaken in the public interest are not.

              Have you noticed that most notices of allowance read the same way? Some form of “Independent claims 1,11 and 21 all contain limitations ABCD. I couldn’t find ABCD in a single reference.” That seems like an odd statement, given that anticipation is insufficient in itself to render something allowable. That’s unfortunate, given that the reasons for allowance would probably be given a substantial amount of weight by any reviewing body.

            6. 7.3.2.1.2.6

              “Utter nonsense. X is X and only X. Y is not X. If one designs around by using Y instead of X you have no issue whatsoever.”

              If only you applied the same logic to the proper scope of awarding X in the first place! Where’s NW “you enable every means by describing one” PA at? I suspect he’d disagree.

              “Y is not X. If one designs around by using Y instead of X you have no issue whatsoever.”

              Unless you stipulate equivilency apparently.

            7. 7.3.2.1.2.7

              RandomGuy, “Matching an engineer with under three months of legal training against someone who went to law school for years, probably took patent or IP courses, and had to pass a certification test doesn’t make for a fair fight in arguments over legal issues, so the viewpoint of most examiners is that it’s not worth it.”

              You make a persuasive case that the junior examiner is not equipped to determine whether a legal argument made by the applicant is a valid argument or not. Therefore if I were the director, I would order the examining corps to ignore legal arguments made by the applicant with the exception of citations to the MPEP. The applicant, if he’s correct on the law, should make the arguments only to those skilled in that art: the Board.

            8. 7.3.2.1.2.8

              Ned errs extremely badly with “Therefore if I were the director, I would order the examining corps to ignore legal arguments made by the applicant with the exception of citations to the MPEP.

              Absolutely the wrong direction to go Ned and directly into lawlessness and chaos.

              You do know that the MPEP is not the law and is only a guideline that binds the examiners in addition to their being required to follow the law, right?

              This has got to be top ten in your most inane things ever uttered. And that is saying a lot.

  2. 6

    Can anybody provide some details regarding how the stipulation came about? It would be interesting to see which party suggested it, which party drafted it, etc. The full text of the stipulation would also be useful to see, if available.

  3. 4

    Anyone who wants to seriously discuss this needs to fold in a discussion of KSR and the protection TO previous patent holders from obvious advances.

        1. 4.1.1.1

          Nice Trolling Leopold.

          It is now a serious discussion because I have added a key Supreme Court ruling that is so often overlooked when the topic come sup.

          Feel free to do your usual running away now.

          1. 4.1.1.1.1

            It is now a serious discussion because I have added a key Supreme Court ruling that is so often overlooked

            You are truly a saint among mortals.

          2. 4.1.1.1.2

            It is now a serious discussion because I have added a key Supreme Court ruling that is so often overlooked when the topic come sup.

            So you’re doubling down on your original insult of Jason’s posting. Nice.

  4. 3

    Regarding this policy discussion:

    Given that a primary rationale for the doctrine of equivalents is to address the problem of after-arising technology, what is the basis for concluding that the DOE also extends to foreseeable technologies, i.e.: those that the patent drafter could have included in the patent. While Ring & Pinion v. ARB does not offer an explanation, the Supreme Court’s opinion in Festo does:

    “The language in the patent claims may not capture every nuance of the invention or describe with complete precision the range of its novelty.” … The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described

    There are two important exceptions to that conclusion which suggest that there is another policy concern that is competing head-to-head with the “humans are fallible so let’s help them out” policy articulated above.

    The first is the foreseeability exception itself when a claim has been amended and prosecution history estoppel applies under Festo. The second is the Fed. Cir.’s own Johnson & Johnston case which holds that equivalents to a claim term that are recited in the patent specification (but not, of course, claimed) are dedicated to the public. The d.o.e. can not be used to capture those disclosed equivalents.

    With respect to this second exception, obvious questions arise such as: what if the equivalents to a claim were disclosed (as equivalents) in a separate application earlier filed by the same applicant? Does Johnson & Johnston apply? What if the unclaimed equivalents were disclosed as equivalents in a publication by the applicant before the filing date of the application? Is there a meaningful distinction that can be drawn between “the applicant failed to claim a disclosed equivalent in the specification” and “the applicant failed to claim or disclose an equivalent known to it”? It seems like a pretty thin distinction to me.

    1. 3.1

      Let’s see.

      Spec discloses a nail and a screw, but claims a nail. First action allowance. No continuations.

      Alleged infringer entitled to use the screw — agreed.

      Now if a reissued is filed within 2 years, I think the patentee can claim the screw.

      So the known interchangeability has to have a caveat — unless the subject matter was intentionally surrendered, either expressly by a narrowing amendment, or by not filing a reissue within two years.

      1. 3.1.1

        Unintended consequence Ned: leave out the screw and have it covered under DOE, resulting in the drive to include even less in patents.

        There is no free lunch from your hypo.

        1. 3.1.1.1

          anon, but this screw-nail problem happens all the time — and it is based on Supreme Court case law.

          After this case, I really am slightly unsure of what the law is with respect to whether the screw is covered under the DOE.

  5. 2

    Nice write up, Dennis.

    Impossible to square this:

    Fed Cir: There is not, nor has there ever been, a foreseeability limitation on the application of the doctrine of equivalents.

    with this:

    Under Festo, the presumption arising from a narrowing amendment can be rebutted if the patentee can show that the equivalent was unforeseeable at the time of amendment. 535 U.S. at 741.

    The first quote is just pure, incompetent sloppiness on the part of the Federal Circuit, one that should be officially corrected by the Federal Circuit immediately.

    1. 2.1

      The first quote is just pure, incompetent sloppiness on the part of the Federal Circuit, one that should be officially corrected by the Federal Circuit immediately.

      I don’t see that. If Festo applies, the doctrine of equivalents does not, so in that case there is no “application of the doctrine of equivalents.”

      1. 2.1.1

        I commend you, LB, for providing the best possible cover for Moore et al.

        But I’m not buying it. Festo and the d.o.e. are joined at the hip. Moreover, Festo doesn’t say that an amendment precludes the d.o.e. It just raises a presumption about its potential application, an application which is certainly “limited” by foreseeability considerations.

  6. 1

    Known interchangeability and foreseeability are effectively the same thing. To exclude the one is to exclude the other.

    Moore is a very clear and logical writer.

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