  United States Court of Appeals
      for the Federal Circuit
                ______________________

SIGMA-TAU HEALTHSCIENCE, INC., AKA SIGMA-
        TAU HEALTHSCIENCE, LLC,
             Plaintiff-Appellant

                          v.

                  UNITED STATES,
                  Defendant-Appellee
                ______________________

                      2016-1125
                ______________________

   Appeal from the United States Court of International
Trade in No. 1:11-cv-00093-GWC, Judge Gregory W.
Carman.
               ______________________

             Decided: September 26, 2016
               ______________________

    JOHN C. MONICA, JR., Porter Wright Morris & Arthur,
Washington, DC, argued for plaintiff-appellant. Also
represented by LESLIE ALAN GLICK, CHRISTOPHER YOOK.

    ALEXANDER J. VANDERWEIDE, Commercial Litigation
Branch, Civil Division, United States Department of
Justice, New York, NY, argued for defendant-appellee.
Also represented by AMY M. RUBIN; BENJAMIN C. MIZER,
JEANNE E. DAVIDSON, Washington, DC; YELENA SLEPAK,
Office of Assistant Chief Counsel, U.S. Customs and
2                     SIGMA-TAU HEALTHSCIENCE, INC.   v. US



Border Protection, United States Department of Home-
land Security, New York, NY.
                 ______________________
    Before NEWMAN, DYK, and REYNA, Circuit Judges.
DYK, Circuit Judge.
    This Customs case concerns the classification of two
chemical products, both stabilized forms of the compound
carnitine, which were imported into the United States by
Sigma-Tau HealthScience, Inc., a.k.a. Sigma-Tau
HealthScience, LLC (“Sigma-Tau”). United States Cus-
toms and Border Protection (“Customs” or “the govern-
ment”) initially classified these products under a
subheading of the Harmonized Tariff Schedule of the
United States (“HTSUS”) that carries a duty. Sigma-Tau
protested, arguing that the products should be classified
under HTSUS heading 2936 (which encompasses “provit-
amins and vitamins”), subheading 2936.29.50, a duty-free
classification.
     The Court of International Trade (“CIT”) concluded
that Sigma-Tau’s products should be classified under a
different subheading, 2923.90.00, making them ineligible
for duty-free treatment. Sigma-Tau HealthScience, Inc. v.
United States (“Sigma-Tau”), 98 F. Supp. 3d 1365, 1377–
78 (Ct. Int’l Trade 2015). On appeal, the parties agree
that the only issue is whether Sigma-Tau’s products are
properly classified as vitamins under HTSUS heading
2936. We agree with Sigma-Tau that its carnitine prod-
ucts are properly classified under that heading, because
carnitine is a vitamin in neonates. We therefore reverse
and remand.
                      BACKGROUND
   Customs classifications according to the headings and
subheadings of the HTSUS determine the duties that
importers must pay to the United States. The question
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                     3



here is the appropriate classification of Sigma-Tau’s
carnitine products.
     Carnitine 1 is a naturally occurring amino acid deriva-
tive and an important nutrient in the human body, where
it serves to transport long-chain fatty acids into mito-
chondria, the centers for energy production within each
cell. Our bodies obtain carnitine exogenously, from food,
and also produce it endogenously, by breaking down and
reforming protein. (According to the Webster Comprehen-
sive Dictionary, an “exogenous” compound originates
outside the organism, while an “endogenous” compound is
one originating or produced internally. See Exogenous,
Webster Comprehensive Dictionary (Int’l ed. 2001); Endog-
enous, id.) Stabilized forms of carnitine are formulated
into tablets or capsules and sold as nutritional supple-
ments; they can also be incorporated into drinks, protein
bars, and other products for human consumption. Car-
nitine is sometimes referred to as “vitamin Bt”; for exam-
ple, the online version of Merriam Webster’s Medical
Dictionary identifies “vitamin Bt” as a synonym of “car-
nitine.” J.A. 1279. While carnitine is an organic com-
pound, it is not listed by name in any heading or
subheading of HTSUS Chapter 29, which covers “Organic
Chemicals.”
    Sigma-Tau imports carnitine products into the United
States. The two carnitine products at issue are acetyl L-
carnitine taurinate hydrochloride with 1.5% silica, which


   1    Carnitine is a chiral compound and exists in two
distinct stereoisomeric forms: the biologically active L-
carnitine enantiomer and the inactive D-carnitine enanti-
omer.     Sigma-Tau’s products specifically contain L-
carnitine, and the parties agree that L-carnitine is the
biologically and commercially significant enantiomer at
issue in this case. For simplicity, we refer hereinafter to
L-carnitine simply as “carnitine.”
4                      SIGMA-TAU HEALTHSCIENCE, INC.   v. US



Sigma-Tau sells under the brand name “L-Tauro,” and
glycine propionyl L-carnitine hydrochloride USP with
1.5% silica, which Sigma-Tau sells under the brand name
“GlycoCarn.” These products, white powders manufac-
tured in Italy, were imported in bulk. In 2010, Customs
classified these products under HTSUS subheading
3824.90.92, which covers “Prepared binders for foundry
molds or cores; chemical products and preparations of the
chemical or allied industries (including those consisting of
mixtures of natural products), not elsewhere specified or
included: Other: Other: Other: Other.” That subheading
carries a 5% duty. Sigma-Tau timely protested this
classification, arguing that the products qualify as vita-
mins under HTSUS subheading 2936.29.50, which covers
“Provitamins and vitamins, natural or reproduced by
synthesis (including natural concentrates), derivatives
thereof used primarily as vitamins, and intermixtures of
the foregoing, whether or not in any solvent: Vitamins
and their derivatives, unmixed: Other vitamins and their
derivatives: Other: Other.” That subheading is duty-free.
     Sigma-Tau brought suit in the CIT, requesting that
the court set aside Customs’ classification decision and
hold that the L-Tauro and GlycoCarn products are proper-
ly classified as vitamins under HTSUS subheading
2936.29.50 (and, therefore, deserving of duty-free treat-
ment). Sigma-Tau also requested that the CIT instruct
Customs to re-liquidate the entries for these products and
to award damages for alleged overpayment of duties.
Sigma-Tau moved for summary judgment. The govern-
ment cross-moved for summary judgment, arguing that
Customs’ initial classification of the merchandise under
HTSUS heading 3824 was erroneous but that HTSUS
subheading 2923.90.00 (covering “Quaternary ammonium
salts and hydroxides; lecithins and other phosphoamino-
lipids, whether or not chemically defined: Other”), not
2936.29.50, was in fact the proper classification.
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                    5



    The CIT found that Sigma-Tau’s products were prima
facie classifiable both as vitamins under HTSUS heading
2936 and as quaternary ammonium salts under heading
2923. Sigma-Tau, 98 F. Supp. 3d at 1374–76. Where an
item is prima facie classifiable under more than one
heading, the General Rules of Interpretation provide
guidance as to which heading should be used. See Dell
Prods. LP v. United States, 642 F.3d 1055, 1057 (Fed. Cir.
2011). Relying on HTSUS General Rule of Interpretation
3 (“GRI 3”), which specifies that when “goods are, prima
facie, classifiable under two or more headings” “[t]he
heading which provides the most specific description shall
be preferred to headings providing a more general de-
scription,” HTSUS, General Notes, at 1, the CIT conclud-
ed that “the term ‘quaternary ammonium salts’ more
specifically describes L-Carnitine than ‘vitamins’” and
thus that Sigma-Tau’s products were properly classified
as quaternary ammonium salts under subheading
2923.90.00, Sigma-Tau, 98 F. Supp. 3d at 1377.
    The CIT consequently granted summary judgment in
favor of the government and denied Sigma-Tau’s motion
for summary judgment. Id. at 1378. Sigma-Tau appeals,
asking us to hold that the proper classification of its
merchandise is under HTSUS subheading 2936.29.50, as
a vitamin.     We have jurisdiction under 28 U.S.C.
§ 1295(a)(5).
                       DISCUSSION
    “The interpretation of the headings and subheadings
of the HTSUS is a question of law, which we review
without deference.” Deckers Corp. v. United States, 532
F.3d 1312, 1314 (Fed. Cir. 2008); see also Airflow Tech.,
Inc. v. United States, 524 F.3d 1287, 1290 (Fed. Cir.
2008). “A classification decision involves two underlying
steps: (1) determining the proper meaning of the tariff
provisions, which is a question of law; and (2) determining
which heading the particular merchandise falls within,
6                      SIGMA-TAU HEALTHSCIENCE, INC.   v. US



which is a question of fact.” Deckers, 532 F.3d at 1314–
15. “We review questions of law de novo, including the
interpretation of the terms of the HTSUS, whereas factu-
al findings of the Court of International Trade are re-
viewed for clear error.” Id. at 1315; see also La Crosse
Tech., Ltd. v. United States, 723 F.3d 1353, 1358 (Fed.
Cir. 2013). However, “if there is no genuine dispute over
the nature of the merchandise, . . . the proper classifica-
tion under which it falls [is] the ultimate question in
every classification case and one that has always been
treated as a question of law.” Bausch & Lomb, Inc. v.
United States, 148 F.3d 1363, 1366 (Fed. Cir. 1998); see
also Gen. Elec. Co.-Med. Sys. Grp. v. United States, 247
F.3d 1231, 1235 (Fed. Cir. 2001).
    The government concedes that the CIT erred when it
applied the rule of relative specificity of GRI 3 to classify
Sigma-Tau’s products. The government acknowledges
that Note 3 to Chapter 29 of the HTSUS (“Chapter Note
3”) is instead applicable. Chapter Note 3 specifies that
“[g]oods which could be included in two or more of the
headings of this chapter are to be classified in that one of
those headings which occurs last in numerical order.”
HTSUS, Ch. 29, Note 3, at 29–1. We have held that “[t]he
Section and Chapter Notes [of the HTSUS] are not op-
tional interpretive rules, but are statutory law.” BenQ
Am. Corp. v. United States, 646 F.3d 1371, 1376 (Fed. Cir.
2011) (internal quotation marks omitted). Consequently,
if Sigma-Tau’s merchandise is prima facie classifiable as
both a quaternary ammonium salt (HTSUS heading 2923)
and as a vitamin (HTSUS heading 2936), Chapter Note 3
dictates that it be classified as the latter, as 2936 “occurs
last in numerical order.”
    Thus, the only issue before us is whether Sigma-Tau’s
L-Tauro and GlycoCarn products are prima facie classifi-
able as vitamins under HTSUS heading 2936. If they are,
that heading applies; if they are not, heading 2923 ap-
SIGMA-TAU HEALTHSCIENCE, INC.    v. US                    7



plies, as both sides agree that the products are prima
facie classifiable as quaternary ammonium salts. 2
                             I
    We first address the government’s contention that the
products are not vitamins because they contain stabi-
lizers. The two products at issue are stabilized forms of
carnitine: acetyl L-carnitine taurinate hydrochloride with
1.5% silica (L-Tauro) and glycine propionyl L-carnitine
hydrochloride, USP with 1.5% silica (GlycoCarn). The
CIT treated the products as equivalent to carnitine itself.
At the CIT, the parties agreed that this was the correct
approach. “The parties agree that the proper classifica-


   2     Before the CIT, Sigma-Tau argued that even if
classified as quaternary ammonium salts under HTSUS
heading 2923, its L-Tauro and GlycoCarn products should
nonetheless qualify for “K designation” and thereby be
granted duty-free treatment because “carnitine” is listed
in the Pharmaceutical Appendix to the HTSUS. “General
Note 13 [of the HTSUS] permits duty free treatment of
certain pharmaceutical products if three requirements are
met . . . .” Forest Labs., Inc. v. United States, 476 F.3d
877, 882 (Fed. Cir. 2007). One requirement of General
Note 13 is that “the merchandise is listed in the Pharma-
ceutical Appendix of the tariff schedule.” Id.
     The CIT concluded that while carnitine itself is indeed
listed in the Pharmaceutical Appendix, the taurine and
glycine components of L-Tauro and GlycoCarn, respective-
ly, are not listed, making L-Tauro and GlycoCarn ineligi-
ble for K designation and thus ineligible for duty-free
treatment under General Note 13. Sigma-Tau, 98 F.
Supp. 3d at 1377. Sigma-Tau does not appeal this aspect
of the CIT’s judgment. The inclusion of carnitine in the
Pharmaceutical Appendix is unrelated to the question of
whether carnitine is prima facie classifiable as a “vita-
min” under HTSUS heading 2936.
8                      SIGMA-TAU HEALTHSCIENCE, INC.   v. US



tion of the two products at issue hinges upon the primary
and only active component of the products, L-Carnitine.”
Sigma-Tau, 98 F. Supp. 3d at 1370. In its briefing at the
CIT, the government described “L-carnitine (or carnitine)”
as “the only biologically active component of the two
products at issue” and indicated that the other chemical
components serve merely as stabilizers, which “render the
two carnitine-based products at issue chemically neutral
and stable.” J.A. 336.
    On appeal, the government agrees that carnitine is
“the sole biologically active component of L-Tauro and
GlycoCarn” but now argues, apparently for the first time,
that “the court erred when it undertook a classification
analysis of L-Carnitine only, and not the actual products
in their imported condition,” i.e., carnitine combined with
stabilizing ingredients. Appellee’s Br. at 28. The gov-
ernment does not articulate a theory as to how the pres-
ence of any particular stabilizing component of L-Tauro or
GlycoCarn (e.g., taurine, glycine, or silica) renders the
products non-vitamins.
     The government’s argument comes too late and is
therefore waived. “Our precedent generally counsels
against entertaining arguments not presented to the
district court.” Golden Bridge Tech., Inc. v. Nokia, Inc.,
527 F.3d 1318, 1322 (Fed. Cir. 2008); see also Singleton v.
Wulff, 428 U.S. 106, 120 (1976). Furthermore, even if the
government had properly raised the argument, the
HTSUS forecloses it. HTSUS heading 2936 explicitly
encompasses “[p]rovitamins and vitamins” and “deriva-
tives thereof used primarily as vitamins,” and Note 1(f) to
Chapter 29 of the HTSUS expressly states that the head-
ings of the chapter cover “[compounds] with an added
stabilizer (including an anticaking agent) necessary for
their preservation or transport.” HTSUS, Ch. 29, Note
1(f), at 29–1.
SIGMA-TAU HEALTHSCIENCE, INC.    v. US                   9



    We thus agree with the CIT that Sigma-Tau’s import-
ed products, L-Tauro and GlycoCarn, should be viewed as
equivalents of carnitine. The proper classification of
carnitine itself determines the proper classification of
Sigma-Tau’s merchandise.
                            II
     Chapter 29 of the HTSUS covers “Organic Chemi-
cals.” Heading 2936 more specifically covers “Provitamins
and vitamins, natural or reproduced by synthesis (includ-
ing natural concentrates), derivatives thereof used pri-
marily as vitamins, and intermixtures of the foregoing,
whether or not in any solvent.” The terms “carnitine” and
“vitamin Bt” do not appear anywhere under heading 2936
or, indeed, anywhere in Chapter 29. Thus, if carnitine is
classifiable as a vitamin under heading 2936, it must be
because it falls within a residual subheading, 2936.29.50
(“Vitamins and their derivatives, unmixed: Other vita-
mins and their derivatives: Other: Other”).
    The CIT construed HTSUS heading 2936 as, in rele-
vant part, an eo nomine provision—i.e., a provision that
describes an article by a specific name, not by use, see
Len-Ron Mfg. Co., Inc. v. United States, 334 F.3d 1304,
1308 (Fed. Cir. 2003). Sigma-Tau, 98 F. Supp. 3d at
1376–77. We agree with the CIT that HTSUS heading
2936 should be treated as an eo nomine provision for
purposes of this case: the operative question here is
whether carnitine qualifies as a “[p]rovitamin[]” or “vita-
min[],” items that are expressly named and covered by
HTSUS heading 2936. 3 Neither party disputes this
interpretation. Because we conclude that HTSUS head-



   3    HTSUS heading 2936 also encompasses “deriva-
tives [of provitamins and vitamins] used primarily as
vitamins”; this separate portion of heading 2936 is proper-
ly read as a use provision.
10                      SIGMA-TAU HEALTHSCIENCE, INC.   v. US



ing 2936 is an eo nomine provision with respect to “vita-
mins,” we need not consider the Carborundum factors,
which pertain only to certain use provisions of the
HTSUS. See Aromont USA, Inc. v. United States, 671
F.3d 1310, 1312–13 (Fed. Cir. 2012); cf. GRK Canada,
Ltd. v. United States, 761 F.3d 1354, 1358 (Fed. Cir.
2014).
     “The first step in properly construing a tariff classifi-
cation term is to determine whether Congress clearly
defined that term in either the HTSUS or its legislative
history.” Airflow Tech., 524 F.3d at 1290–91 (quoting
Russell Stadelman & Co. v. United States, 242 F.3d 1044,
1048 (Fed. Cir. 2001)). In this instance, there is no clear
definition of “vitamin” within Chapter 29 or its legislative
history. We have held that,
     [w]hen, as here, a tariff term is not defined in ei-
     ther the HTSUS or its legislative history, the
     term’s correct meaning is its common or diction-
     ary meaning in the absence of evidence to the con-
     trary. We have explained that, to determine the
     common meaning of a tariff term, a court may rely
     upon its own understanding of terms used, and
     may consult standard lexicographic and scientific
     authorities.
Id. at 1291 (citation, alterations, and internal quotation
marks omitted). “To discern the common meaning of a
tariff term, we may consult dictionaries, scientific author-
ities, and other reliable information sources.” Kahrs Int’l,
Inc. v. United States, 713 F.3d 640, 644 (Fed. Cir. 2013).
To the extent that dictionaries or other extrinsic refer-
ences disagree with one another, a court may “properly
rel[y] on the definition most commonly found in the
lexicographical sources to derive the common meaning of
this term.” Len-Ron, 334 F.3d at 1310.
    Here the CIT’s decision that carnitine is prima facie
classifiable as a vitamin rested on the fact that carnitine
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                    11



is alternatively known as “vitamin Bt.” “[T]he Court finds
that since L-Carnitine is commonly known as vitamin Bt
it is prima facie classifiable in HTSUS heading 2936.”
Sigma-Tau, 98 F. Supp. 3d at 1376. Similarly, the gov-
ernment argues in support of the opposite result that
carnitine cannot be a vitamin because many respected
scientific sources do not include carnitine in listings of
commonly accepted vitamins. The government notes, for
example, that a National Import Specialist for Customs
testified with regard to Sigma-Tau’s carnitine products
that “the FDA does not indicate they’re vitamins,” nor did
the scientific literature he had reviewed. J.A. 750.
    Whether a substance is commonly referred to as a
“vitamin” may be pertinent, but only if there is a consen-
sus as to the use of that terminology. See Len-Ron, 334
F.3d at 1310 (holding that the common meaning of the
HTSUS term “vanity case” should not be limited to cases
that include mirrors, as the record showed that the public
uses the term to refer to a variety of cases, with no con-
sensus that the term “requires that the case be fitted with
a mirror”); Nippon Kogaku (USA), Inc. v. United States,
673 F.2d 380, 382, 384 (CCPA 1982) (holding that a
certain type of optical microscope should be classified
under a particular tariff heading because, inter alia, the
CIT had found that “without contradiction, industry, as
well as ophthalmologists and optometrists, principal users
of the merchandise, refer to it as a slit-lamp microscope or
a slit-lamp, not as a compound microscope”); see also
CamelBak Prods., LLC v. United States, 649 F.3d 1361,
1368 (Fed. Cir. 2011) (holding that “how the subject
articles are regarded in commerce” and “how the subject
articles are described in sales and marketing literature”
can “guide the court’s assessment of whether articles fall
within the scope of an eo nomine provision”). There is no
such consensus here. We must, therefore, determine
whether carnitine is a “vitamin” under HTSUS heading
12                    SIGMA-TAU HEALTHSCIENCE, INC.   v. US



2936, applying the commonly accepted definition of the
term “vitamin.” 4
    Indeed, HTSUS heading 2936 contemplates such an
inquiry. By its very terms the heading covers not only
approximately one dozen expressly named vitamins 5 but
also open-ended categories of further “Vitamins and their
derivatives,” including “Other vitamins and their deriva-
tives: Other: Aromatic or modified aromatic” (HTSUS
subheading 2936.29.20) and “Other vitamins and their
derivatives:    Other:   Other”     (HTSUS     subheading
2936.29.50). While Explanatory Notes to HTSUS head-
ings are non-binding (see infra), the Explanatory Note to
heading 2936 states in its “List of products which are to
be classified as provitamins or vitamins within the mean-



     4   This is not a case in which Customs or the im-
porter contends that the term in question has a special
commercial meaning distinct from its common meaning.
See Carl Zeiss, Inc. v. United States, 195 F.3d 1375, 1379
(Fed. Cir. 1999) (“One who argues that a tariff term
should not be given its common or dictionary meaning
must prove that it has a different commercial meaning
that is definite, uniform, and general throughout the
trade.”); see also Nix v. Hedden, 149 U.S. 304, 306 (1893)
(“There being no evidence that the words ‘fruit’ and
‘vegetables’ have acquired any special meaning in trade or
commerce, they must receive their ordinary meaning.”)
    5    The individual vitamins expressly included under
HTSUS subheading 2936 are vitamin A (2936.21.00),
vitamin B1 (2936.22.00), vitamin B2 (2936.23.00), D- or
DL-pantothenic acid (vitamin B3 or vitamin B5,
2936.24.00), vitamin B6 (2936.25.00), vitamin B12
(2936.26.00), vitamin C (2936.27.00), vitamin E
(2936.28.00), folic acid (2936.29.10), niacin and niacina-
mide (2936.29.15), vitamin D (2936.29.50.20), and biotin
(2936.29.50.30).
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                     13



ing of heading 29.36” that “[t]he list of products in each of
the following groups is not exhaustive” and that “[t]he
products listed are examples only.” Explanatory Notes to
the Harmonized Commodity Description and Coding
System 29.36 (5th ed. 2012) (“EN 29.36”). Explanatory
Note 29.36 also includes a list of “Exclusions,” products
“which, though sometimes called vitamins, have no vita-
min activity or have a vitamin activity which is of second-
ary importance in relation to their other uses” and thus
are not classifiable under HTSUS 2936. Id. Among the
excluded products are various compounds whose names
include the word “vitamin,” such as “Vitamin H1,” “Vita-
min B4,” and “Vitamin F.” Id. (Carnitine (or vitamin Bt)
is not included among the “Exclusions.” Id.) The note
thus makes clear that the mere use of the term “vitamin”
to refer to a particular compound is not conclusive. At the
same time, the universe of compounds prima facie classi-
fiable as vitamins under heading 2936 cannot be limited
to only those compounds that are explicitly listed under
the heading.
    We thus look to the definition of “vitamin” and ask
whether carnitine falls within the definition. “Determin-
ing the proper classification requires first construing the
relevant provisions of the schedule and then deciding
which provision encompasses the merchandise at issue.”
Del Monte Corp. v. United States, 730 F.3d 1352, 1354
(Fed. Cir. 2013); see also Airflow Tech., 524 F.3d at 1291.
Before the CIT, the government urged that the court
apply the definition of “vitamin” in the Explanatory Note:
    Vitamins are active agents, usually of complex
    chemical composition, which are obtained from
    outside sources and are essential for the proper
    functioning of human or other animal organisms.
    They cannot be synthesised by the human body
    and must therefore be obtained in final or nearly
    final form (provitamins) from outside sources.
    They are effective in relatively minute amounts
14                      SIGMA-TAU HEALTHSCIENCE, INC.   v. US



     and may be regarded as exogenous biocatalysts,
     their absence or deficiency giving rise to metabolic
     disturbances or “deficiency diseases.”
EN 29.36 (emphasis added). The government contended
at the CIT that because carnitine can be synthesized in
the human body, it is not a vitamin under the definition of
EN 29.36. But Explanatory Notes are not Chapter Notes
or Section Notes and are not binding. Explanatory Notes
“may be generally useful as guides to the scope of unclear
HTSUS headings, [but] they are not legally binding.”
Archer Daniels Midland Co. v. United States, 561 F.3d
1308, 1315 (Fed. Cir. 2009) (internal quotation marks
omitted); see also E.T. Horn Co. v. United States, 367 F.3d
1326, 1329 (Fed. Cir. 2004) (Explanatory Notes are “not
controlling” but “provide interpretive guidance”). “Alt-
hough the examples in the Explanatory Notes are proba-
tive and sometimes illuminating, we shall not employ
their limiting characteristics, to the extent there are any,
to narrow the language of the classification heading
itself.” Rubie’s Costume Co. v. United States, 337 F.3d
1350, 1359 (Fed. Cir. 2003).
    Explanatory Note 29.36, in defining vitamins as com-
pounds that “cannot be synthesised by the human body,”
cannot be correct, since vitamin D is unambiguously
included under the heading: subheading 2936.29.50.20
expressly names “Vitamins D and their derivatives.” And
undisputed evidence establishes that vitamin D can be
synthesized, in limited and generally inadequate
amounts, by the human body. See Sigma-Tau, 98 F.
Supp. 3d at 1375–76. This portion of the definition of
“vitamin” in EN 29.36 thus contradicts the express inclu-
sion of vitamin D under HTSUS heading 2936 and must
be disregarded, as the CIT correctly held. Id. at 1376.
Explanatory Note 29.36 is also inconsistent with the
prevailing definitions of “vitamin” in various scientific
references cited by the parties, all of which define a
vitamin as a compound that is not produced by the human
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                     15



body in amounts “sufficient” or “adequate” for healthy
function. 6 The parties indeed agree that the definition of



   6     The definitions of “vitamin” presented by the par-
ties are as follows. Sigma-Tau’s expert submitted a report
presenting definitions from two textbooks:
   (From The Vitamins:) A vitamin: (i) is an organic
   compound distinct from fats, carbohydrates, and
   proteins; (ii) is a natural component of foods in
   which it is usually present in minute amounts;
   (iii) is essential, usually in minute amounts, for
   normal physiological function (i.e., maintenance,
   growth,      development,     and/or    production);
   (iv) causes, by its absence or underutilization, a
   specific deficiency syndrome; and (v) is not synthe-
   sized by the host in amounts adequate to meet
   normal physiological needs.
   (From Nutrition Now:) Vitamins are chemical
   substances that perform specific functions in the
   body. They are essential nutrients because, in
   general, the body cannot produce them or [cannot]
   produce sufficient amounts of them.
J.A. 288 (Expert Report of Yesu T. Das, quoting Gerald F.
Combs, Jr., The Vitamins 4 (4th ed. 2012) (J.A. 291) and
Judith E. Brown, Nutrition Now 20–2 (7th ed. 2014) (J.A.
292)) (alteration and emphasis in original, underscoring
added).
    The government introduced definitions from two
chemical encyclopedias:
   Vitamins are specific organic compounds that are
   essential for normal metabolism. These micronu-
   trients are not synthesized by humans, either at all
   or in sufficient quantity, and must be obtained
   from the diet or as synthetic supplements.
16                     SIGMA-TAU HEALTHSCIENCE, INC.   v. US



EN 29.36 is too restrictive in this respect. For example,
the government proposes defining “vitamins” as “those
organic compounds which are essential for human health,
but must be provided or supplemented from an exogenous
source because the human body cannot normally synthe-
size the compounds, either sufficiently or at all.” Appel-
lee’s Br. at 14 (emphasis added).           Moreover, the
definitions provided by both parties are consistent with
each other. We therefore adopt, as the definition of “vit-
amin,” the following: vitamins are organic chemical
substances that are essential micronutrients because, in
general, the body cannot produce them or produce suffi-
cient amounts of them.
     While agreeing to this general definition, the parties
still differ as to the proper scope of this definition in
certain respects. First, Sigma-Tau argues that “vitamin”
should not be limited to compounds that are required by
individuals with normal function but should also encom-
pass those required by individuals with abnormal func-
tion. We reject this argument. Literature definitions
introduced by both parties emphasize the fact that a
vitamin is a substance required for normal physiological



J.A. 778 (reproducing the Concise Encyclopedia of Chem.
Tech. 2092 (4th ed. 1999)) (emphasis added).
     Vitamins are essential, organic compounds which
     are either not synthesized in the human and ani-
     mal organism or formed only in insufficient
     amounts. Therefore, they must be regularly con-
     sumed with the diet either as such or as a precur-
     sor (provitamin) that can be converted to the
     vitamin in the body. . . . Vitamins are classified
     not chemically but by their activity.
J.A. 780 (reproducing Ullmann’s Encyclopedia of Indus.
Chemistry vol. 38, 112 (6th ed. 2003)) (emphasis added).
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                  17



function. See J.A. 291 (The Vitamins: “essential . . . for
normal physiological function”; “not synthesized by the
host in amounts adequate to meet normal physiological
needs” (emphasis added)); J.A. 292 (Nutrition Now: “es-
sential nutrients because, in general, the body cannot
produce them or produce sufficient amounts of them”
(emphasis added)); J.A. 778 (Concise Encyclopedia of
Chem. Tech.: “specific organic compounds that are essen-
tial for normal metabolism” (emphasis added)). The
correct definition of “vitamin” thus leaves out compounds
that might be essential to individuals with abnormal
physiological function, e.g., those suffering from rare
genetic disorders or organ failure.
    Second, the government appears to argue that the
proper definition of “vitamin” refers only to compounds
that cannot be synthesized in sufficient amounts by
human adults. On the contrary, Sigma-Tau argues that
the proper definition of “vitamin” must not be limited to
compounds essential to adults but should also include
compounds that children and infants require for normal,
healthy function. We agree with Sigma-Tau that there is
no reason to limit “vitamin” to compounds required by
adults rather than children. Neither the definition of EN
29.36 nor any of the literature definitions presented by
either party is expressly limited to adults. Moreover, the
definition in The Vitamins describes “vitamins” as com-
pounds “essential” for “maintenance, growth, develop-
ment, and/or production,” J.A. 291 (emphasis added); the
inclusion of “growth” and “development” suggests that
compounds required by children—i.e., those who are
“growing” and “developing”—should be included even if
not required by adults.
                             III
    Having defined “vitamin,” we turn to whether car-
nitine is prima facie classifiable as such under HTSUS
heading 2936. We hold, based on the undisputed evidence
18                     SIGMA-TAU HEALTHSCIENCE, INC.   v. US



of record, that the CIT’s conclusion on this point was
correct: carnitine is prima facie classifiable as a vitamin.
     Sigma-Tau argues that the evidence shows that “cer-
tain human populations, including children and neonates,
require an exogenous source of L-Carnitine.” Appellant’s
Reply Br. at 14. Sigma-Tau introduced uncontroverted
evidence establishing that infants, including neonates
(infants less than four weeks old), require exogenous
sources of carnitine for healthy growth and cannot syn-
thesize adequate quantities endogenously. One scientific
article states that “[n]eonates rely on an exogenous supply
of L-carnitine because their capacity for endogenous
synthesis is still poorly developed.”        J.A. 1089 (J.
Harmeyer, The Physiological Role of L-Carnitine, 27
Lohmann Info. 1, 7 (2002)). A second article states that
“certain pediatric populations, specifically neonates and
infants, have decreased biosynthetic capacity and are at
risk of developing carnitine deficiency, particularly when
receiving PN [(parenteral nutrition)]” and that
“[a]lthough carnitine is considered a nonessential nutrient
in adults, it may be considered a conditionally essential
nutrient in pediatric populations, particularly neonates
receiving PN.” J.A. 1091, 1094 (Catherine M. Crill &
Richard A. Helms, The Use of Carnitine in Pediatric
Nutrition, 22 Nutrition in Clinical Practice 204, 207
(2007)).
     The scientific authorities cited by the government do
not directly address the question of whether carnitine
qualifies as a vitamin with respect to infants. They
merely state that carnitine is not recognized as a vitamin
in adults, as adults are able to synthesize adequate quan-
tities of carnitine from other components of their diet.
For example, the book Recommended Dietary Allowances,
a publication of the National Research Council introduced
by the government, states that “[carnitine] has not been
demonstrated to be a vitamin for the healthy adult hu-
man” but adds that “the newborn infant appears to have
SIGMA-TAU HEALTHSCIENCE, INC.   v. US                    19



reduced stores of carnitine as well as a low capacity for
synthesizing it” and that “[s]everal laboratories are inves-
tigating the possibility that carnitine may be an essential
nutrient for the newborn, especially for those born prema-
turely.” J.A. 789, 790 (Recommended Dietary Allowances
265, 266 (10th ed. 1989)). At argument the government
conceded that the evidence shows that infants, and neo-
nates in particular, require exogenous sources of carnitine
for normal, healthy function.
    In view of this evidence, the CIT correctly held that
carnitine is prima facie classifiable as a vitamin. Undis-
puted evidence in the record shows that carnitine is an
organic compound essential for neonates (infants less
than four weeks old). They rely on an exogenous supply of
L-carnitine because their ability to synthesize it endoge-
nously is still poorly developed.
                       CONCLUSION
    For the foregoing reasons, carnitine and Sigma-Tau’s
imported merchandise are prima facie classifiable as a
vitamin under HTSUS heading 2936. As noted above,
under Chapter Note 3, “[g]oods which could be included in
two or more of the headings of this chapter are to be
classified in that one of those headings which occurs last
in numerical order.” We thus hold that carnitine, and
Sigma-Tau’s products, are properly classified as a vitamin
under HTSUS heading 2936, in residual subheading
2936.29.50, rather than as a quaternary ammonium salt
under HTSUS heading 2923. We conclude that the CIT
erred in denying Sigma-Tau’s motion for summary judg-
ment and in granting summary judgment to the govern-
ment. We reverse and remand for further proceedings
consistent with this opinion.
            REVERSED AND REMANDED
                          COSTS
   No costs.
