       NOTE: This disposition is nonprecedential.


  United States Court of Appeals
      for the Federal Circuit
                ______________________

  TWIN PEAKS SOFTWARE INC., A CALIFORNIA
              CORPORATION,
              Plaintiff-Appellant

                           v.

        IBM CORPORATION, A NEW YORK
                CORPORATION,
                Defendant-Appellee
              ______________________

                      2016-2177
                ______________________

   Appeal from the United States District Court for the
Northern District of California in No. 3:14-cv-03933-JST,
Judge Jon S. Tigar.
                 ______________________

                Decided: May 26, 2017
                ______________________

    BRUCE JOSHUA WECKER, Hausfeld LLP, San Francis-
co, CA, argued for plaintiff-appellant.

    ANDREW J. BRAMHALL, Quinn Emanuel Urquhart &
Sullivan, LLP, Redwood Shores, CA, argued for defend-
ant-appellee. Also represented by ROBERT WILLIAM STONE,
BRICE CLARK LYNCH.
                 ______________________
2              TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION




    Before PROST, Chief Judge, LOURIE and STOLL, Circuit
                          Judges.
LOURIE, Circuit Judge.
    Twin Peaks Software Inc. (“Twin Peaks”) appeals
from a judgment of the United States District Court for
the Northern District of California that claims 1 and 4 of
U.S. Patent 7,418,439 (“the ’439 patent”) are invalid as
indefinite following a claim construction order by the
district court. See Twin Peaks Software Inc. v. IBM Corp.,
No. 3:14-cv-03933-JST, 2016 WL 1409748 (N.D. Cal. Apr.
11, 2016) (“Order”). Because the district court did not err
in its claim construction or in concluding that the chal-
lenged claims are invalid as indefinite, we affirm.
                       BACKGROUND
    Twin Peaks owns the ’439 patent, which is directed to
“a virtual file system that links two or more file systems
together and mirrors between them in real time,” which is
called a “mirror file system,” or “MFS.” See ’439 patent,
Title, Abstract. According to the ’439 patent, the inven-
tion provides “a new approach for mounting a file system
on a directory” and allows two file systems to be “linked
together and become a mirroring pair” so that “the previ-
ous contents of the [same] mounted directory are not
hidden,” and once the MFS mounting is accomplished, the
mounted file systems are “under the management of” “the
MFS.” Id. col. 3 ll. 16–17, col. 10 ll. 44–51.
    Twin Peaks asserted the ’439 patent, including inde-
pendent claims 1 and 4, against IBM Corp. (“IBM”),
alleging that IBM’s products using “a technology called
both ‘Panache’ and ‘Active File Management’” infringe the
’439 patent. Order, 2016 WL 1409748, at *1. Claim 1 of
the ’439 patent reads as follows:
     1. A virtual file system which provides mirroring
     and linking of two file systems, comprising:
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION            3



       means for mounting components of each of
       said two file systems on a single mount
       point constituting a single root directory
       for the components of both of said two file
       systems such that each mounted compo-
       nent of one of said two file systems is
       linked together with and becomes a mirror-
       ing pair with a corresponding mounted
       component in the other one of said two file
       systems, each of said two file systems hav-
       ing an application interface data structure
       constituting a programming interface for
       management thereof and access thereto;
       and
       a virtual file system configured to manage
       the linking and mirroring of the corre-
       sponding mounted components of each of
       said two file systems, and including a su-
       per application interface data structure
       containing an application interface data
       structure of said virtual file system, and
       said application interface data structures
       of each of said two file systems.
’439 patent, col. 18 ll. 35–53 (emphasis added). Claim 4 of
the ’439 patent reads as follows:
   4. A method for mirroring files and directories be-
   tween file systems on a computer system or on
   two computer systems connected to each other via
   a network, comprising the steps of:
       mounting components of each of two file
       systems on a single mount point constitut-
       ing a single root directory to create a vir-
       tual file system in which each mounted
       component of one of said two file systems
       is linked together with a corresponding
       component in the other one of said two file
4             TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION



        systems, each of said mounted components
        being one of a directory and a file;
        configuring said virtual file system so that
        each component of said virtual file system
        has a super application interface data
        structure containing an application inter-
        face data structure of said component in
        said virtual file system, an application in-
        terface data structure of a linked compo-
        nent in said one of said two file systems,
        and an application interface data struc-
        ture of said corresponding linked compo-
        nent in said other one of said two file
        systems, said application interface data
        structure of said component in said virtual
        file system providing a mechanism for
        managing said component within said vir-
        tual file system and the corresponding
        linked components within said two file sys-
        tems;
        upon receiving a request to perform a
        write operation on one of said mounted
        components, using said application inter-
        face data structure of said component in
        said virtual file system to perform the
        write operation on said linked component
        in said one of said two file systems and on
        the corresponding linked component in
        said other one of said two file systems in
        real time in response to said request.
Id. col. 19 ll. 1–33 (emphasis added).
   The district court held a claim construction hearing
and construed, inter alia, the two limitations highlighted
above, which we will here refer to as the “means for
mounting” limitation of claim 1 and the “mechanism for
managing” limitation of claim 4, respectively. The district
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION            5



court analyzed both of the limitations as means-plus-
function limitations under 35 U.S.C. § 112 ¶ 6. 1 See
Order, 2016 WL 1409748, at *5, *11.
     As for the “means for mounting” limitation, Twin
Peaks argued that relevant structure is disclosed in
various parts of the specification, including a portion that
discusses the “MFS mount protocol.” See J.A. 122–25
(citing ’439 patent, col. 10 l. 32–col. 12 l. 14). IBM re-
sponded that the specification only discloses the result of
the “MFS mount protocol,” without disclosing how to
achieve that result, and that Twin Peaks failed to “iden-
tif[y] any specific algorithm.” J.A. 651–52 (emphasis
omitted).
    The district court agreed with IBM. The court noted
that, although the specification discusses “the outcome
after a system administrator implements the MFS mount-
ing protocol,” it “only recites functional, rather than
structural language” and fails to “disclose how to perform
the command” so that the two file systems mounted on a
single mounting point remain available and unhidden.
Order, 2016 WL 1409748, at *7 (emphases in original).
As such, the district court determined that the “means for
mounting” limitation was indefinite. Id.
    Regarding the “mechanism for managing” limitation,
Twin Peaks argued that the specification provides suffi-
cient disclosure of the limitation by way of an example of
the “open” operation and explanations as to how other
operations “follow the same procedure.” J.A. 130–31.
Twin Peaks further submitted to the district court expert



   1     The ’439 patent was filed before the effective date
of the Leahy-Smith America Invents Act, Pub. L. No. 112-
29, § 3, 125 Stat. 284, 285–93 (2011), and it is governed by
the prior version of § 112, see Fleming v. Escort, Inc., 774
F.3d 1371, 1374 n.1 (Fed. Cir. 2014).
6              TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION



declarations stating that “one skilled in the art would
easily have been able to code these data structures and
operations” and providing the “actual source code one
skilled in the art would produce” for the close, read, and
write operations. J.A. 1240–42. IBM responded that the
’439 patent discloses only one operation, i.e., “open,” out of
30–40 operations, although the ’439 patent notes that
implementing certain other operations, e.g., “write,”
would be different from the “open” operation. J.A. 655–
56.
    The district court rejected Twin Peaks’s argument and
agreed with IBM that the ’439 patent discloses insuffi-
cient structure of the managing function. Order, 2016 WL
1409748, at *12. The court determined that the specifica-
tion “discloses the code for one operation in the managing
function—the open operation (mfs_open),” id.; however,
the court noted that “the open operation is a partial but
inadequate guide for other operations” and that “[t]he
specification fails to delineate the operations encompassed
by the managing function,” id. at *13. Therefore, the
district count concluded that the specification failed to
provide sufficient disclosure “to render the bounds of the
claim understandable to one of ordinary skill in the art”
and that the “mechanism for managing” limitation was
indefinite. Id. at *13–14 (citation and internal quotation
marks omitted).
   Twin Peaks timely appealed. We have jurisdiction
pursuant to 28 U.S.C. § 1295(a)(1).
                        DISCUSSION
    On appeal, Twin Peaks challenges the district court’s
indefiniteness determinations of claims 1 and 4. We
review the district court’s conclusion of indefiniteness de
novo, see Interval Licensing LLC v. AOL, Inc., 766 F.3d
1364, 1370 (Fed. Cir. 2014), and underlying factual de-
terminations that are based on extrinsic evidence for clear
error, Williamson v. Citrix Online, LLC, 792 F.3d 1339,
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION            7



1246 (Fed. Cir. 2015) (citing Teva Pharm. USA, Inc. v.
Sandoz, Inc., 135 S. Ct. 831, 840–41 (2015)).
     As an initial matter, the parties do not dispute that
the “means for mounting” and “mechanism for managing”
limitations are means-plus-function limitations governed
by § 112 ¶ 6. Appellant’s Br. 8; Appellee’s Br. 27; see
Order, 2016 WL 1409748, at *5, *11. If a claim contains a
means-plus-function limitation, and the written descrip-
tion lacks structure for those means, we have held that
the claim is indefinite and hence invalid. E.g., Biomedino,
LLC v. Waters Techs. Corp., 490 F.3d 946, 950–53 (Fed.
Cir. 2007). Therefore, we proceed to “attempt to construe
the disputed claim term by identifying the corresponding
structure, material, or acts described in the specification
to which the claim term will be limited.” Robert Bosch,
LLC v. Snap-On Inc., 769 F.3d 1094, 1097 (Fed. Cir. 2014)
(citation and internal quotation marks omitted).
    Twin Peaks contends that the ’439 patent specifica-
tion discloses sufficient structure for the respective
means-plus-function limitations of claims 1 and 4. We
discuss each limitation in turn.
                 I. “Means for Mounting”
    Regarding claim 1, Twin Peaks argues that what the
district court identified as a functional description of the
“means for mounting” limitation is actually the structure
corresponding to the limitation. Twin Peaks points to,
inter alia, the ’439 patent’s disclosure of the “mfs_vfs”
data structure, which is reproduced below:
8             TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION




Appellant’s Br. 19–20 (citing ’439 patent, col. 11 ll. 6–14).
Twin Peaks also points to the ’439 patent specification
describing that “[t]he MFS mount operation sets up the
data structure mfs_vfs to contain the vfs data structures”
and that “[t]he MFS inherits all of the contents of the
mounted directory into its mfs_vfs virtual file system data
structure.” Id. at 19–22 (citing ’439 patent, col. 10 ll. 52–
54, col. 11 ll. 43–45).
     Based on these disclosures in the specification, Twin
Peaks contends on appeal that what constitutes the
structure corresponding to the “means for mounting”
limitation is a two-step algorithm of: (1) “set[ting] up” the
“mfs_vfs” data structure to link two “vfs” structures; and
(2) “inherit[ing]” the content of the two linked “vfs” data
structures. Id. at 36–37. With this understanding of the
“means for mounting” limitation, according to Twin
Peaks, claim 1 is not indefinite because “some structure is
disclosed” and “the implementation of the steps of the
algorithm [is] to be measured by the understanding and
enablement of one skilled in the art.” Id. at 44.
    IBM responds that, although Twin Peaks refers to
multiple columns and figures of the ’439 patent, it fails to
identify any algorithm that is clearly linked or associated
with the “means for mounting” function, and that all of
the descriptions identified by Twin Peaks disclose the
outcome of, or what results from, the MFS mounting
function. IBM also contends that Twin Peaks is improp-
erly relying on the knowledge of one of ordinary skill in
the art to “fill in gaps in disclosure.” Id. at 35–36.
     We agree with IBM that the ’439 patent does not dis-
close a structure corresponding to the “means for mount-
ing” limitation. Twin Peaks’s argument focuses on the
“MFS Mount Protocol” section of the ’439 patent. Parts of
the “MFS Mount Protocol” section, ’439 patent, col. 10
l. 32–col. 12 l. 14, do appear to indicate that a detailed
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION              9



description of the MFS mount algorithm or structure
would follow; the specification states that the MFS
mounting protocol “provides a new approach for mounting
a file system on a directory,” id. col. 10 ll. 44–45, and what
“the MFS can do” to “link up . . . two file structures and
make them a mirroring pair,” id. col. 11 ll. 31–33. How-
ever, the “means for mounting” limitation is circularly
described by referring to the very term “mount” and the
results of various “mount” operations, rather than by
disclosing the identity of the “means for mounting.”
    Twin Peaks appears to argue that the “MFS Mount
Protocol” involves multiple regular mount operations
known in the art, but even assuming arguendo that that
contention is accepted, the specification does not describe
to what extent the MFS mount protocol involves the
regular mount operations or to what extent the “MFS
mount” operation is different from the regular “mount”
operation. See Biomedino, 490 F.3d at 953 (holding that
“a bare statement that known techniques or methods can
be used does not disclose structure”); Med. Instrumenta-
tion & Diagnostics Corp. v. Elekta AB, 344 F.3d 1205,
1211 (Fed. Cir. 2003) (noting “[t]he requirement that a
particular structure be clearly linked with the claimed
function in order to qualify as corresponding structure”).
    Twin Peaks faults the district court for misunder-
standing the MFS mount operation and argues that how
the MFS mount operation is performed, rather than the
result of it, is described by disclosing the data structure,
“mfs_vfs,” and its contents. Appellant’s Br. 39. However,
Twin Peaks cannot, and does not appear to, argue that
the corresponding structure of the “means for mounting”
limitation is the “mfs_vfs” data structure itself, which the
district court determined describes another element of
claim 1 and is not at issue on appeal. See Default Proof
Credit Card Sys., Inc. v. Home Depot U.S.A., Inc., 412
F.3d 1291, 1299–1300 (Fed. Cir. 2005) (noting that the
structure identified by the party corresponds to a sepa-
10             TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION



rately claimed element and cannot correspond to the
means-plus-function limitation in question).
     Instead, Twin Peaks argues that the steps of “setting
up” the “mfs_vfs” data structure and “inheriting” the
contents according to the “mfs_vfs” data structure setup
correspond to how the MFS mounting operation is per-
formed. However, the ’439 patent specification does not
describe the MFS mounting algorithm as this two-step
process or any other process. As discussed above, the ’439
patent specification does not adequately disclose what
algorithm or other structure corresponds to the “means
for mounting” limitation. Biomedino, 490 F.3d at 952
(noting that “structure supporting a means-plus-function
claim under § 112, ¶ 6 must appear in the specification”
and that the proper analysis “asks first whether structure
is described in the specification” (emphasis in original)
(citation omitted)). In arguing that the “means for mount-
ing” limitation is a two-step process of “setting up” and
“inheriting” steps, Twin Peaks pieces together disparate
portions of the specification to conjure up a corresponding
structure. We find that argument unpersuasive.
    Lastly, Twin Peaks argues that a person of ordinary
skill in the art reading the specification would understand
what structure corresponds to the “means for mounting”
limitation and could implement it because “some struc-
ture is disclosed” and therefore, omitting certain details is
“of no significance.” Appellant’s Br. 44. Twin Peaks cites
our case law holding that, in some cases, disclosure of
“some structure” can be sufficient, e.g., Atmel Corp. v.
Info. Storage Devices, Inc., 198 F.3d 1374, 1382 (Fed. Cir.
1999), as supporting its proposition. However, the “some
structure” in the specification that would be sufficient still
should be “some structure corresponding to the means”
recited in the claims “so that one can readily ascertain
what the claim means and comply with the particularity
requirement of ¶ 2.” Atmel, 198 F.3d at 1382 (emphasis
added). Indeed, the “interpretation of what is disclosed
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION              11



must be made in light of the knowledge of one skilled in
the art,” but “the understanding of one skilled in the art
in no way relieves the patentee of adequately disclosing
sufficient structure in the specification.” Id. at 1380; see
also Biomedino, 490 F.3d at 952. Here, as discussed
above, other than the post hoc synthesis of what the
“means for mounting” limitation corresponds to as pro-
posed by Twin Peaks, the ’439 patent specification itself
does not adequately disclose the corresponding structure
of the “means for mounting” limitation, and that inade-
quate disclosure cannot be cured simply by relying on the
knowledge of a person skilled in the art. Biomedino, 490
F.3d at 953 (“The inquiry is whether one of skill in the art
would understand the specification itself to disclose a
structure, not simply whether that person would be
capable of implementing a structure.” (citation omitted)).
    We therefore conclude that the “means for mounting”
limitation of claim 1 is indefinite and that the district
court did not err in so concluding.
              II. “Mechanism for Managing”
     Regarding claim 4, Twin Peaks argues that the dis-
trict court misunderstood the claimed mechanism for
managing, and according to the correct understanding,
disclosure of source code for any file operations, much less
for the entire set of file operations, is not necessary. Here,
Twin Peaks points to, inter alia, a section of the ’439
patent, entitled “File/Directory Operations,” and contends
that the structure corresponding to the claimed mecha-
nism for managing entails the MFS system intercepting
the system calls through the “mnode” structure, which is
reproduced below:
12            TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION




Appellant’s Br. 22 (citing ’439 patent, col. 12 ll. 47–56).
Based on this disclosure, Twin Peaks argues that the
structure corresponding to the “mechanism for managing”
entails a two-step algorithm of: (1) receiving file opera-
tions through the “mnode” structure; and (2) directing or
routing the file operations to the underlying file systems
accordingly. Id. at 47–48. Furthermore, Twin Peaks
contends that the ’439 patent goes beyond what is neces-
sary in disclosing the code for the “mfs_open” operation,
which is reproduced below:
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION             13




Id. at 23 (citing ’439 patent, col. 13 ll. 26–50); id. at 51.
According to Twin Peaks, this disclosure of the
“mfs_open” operation and the ’439 patent’s explanation
that “[a]ll other operations like mfs_read( ), mfs_write( ),
mfs_setattr( ), mfs_close( ), etc., follow the same procedure
as described in mfs_open( )” are “more than what would
be necessary for one skilled in the art to understand the
algorithm.” Id. at 52–54 (citing ’439 patent, col. 13 ll. 52–
54). Therefore, Twin Peaks argues that the “mechanism
for managing” limitation should be interpreted as a single
function with a corresponding two-step process, and
14            TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION



disclosure of particular file operations source code is not
necessary; at any rate, the ’439 patent discloses more
than enough.
     IBM responds that the district court correctly deter-
mined that the disclosure in the ’439 patent is insufficient
because the “mechanism for managing” function, although
a single function, includes multiple file operations, the
full scope of which are not disclosed in the specification.
IBM also contends that the district court correctly found
that the disclosure of the “mfs_open” operation and the
accompanying explanation to “follow the same procedure”
are inadequate. For example, IBM argues that the
“write” operation source code provided by Twin Peaks’s
expert “follow[ing] the same procedure” is missing a key
feature of the invention and demonstrates that inadequa-
cy.
     We agree with IBM that the ’439 patent does not pro-
vide sufficient structure corresponding to the “mechanism
for managing” limitation. To the extent that Twin Peaks
contends that the “mechanism for managing” entails a
two-step process of receiving and directing operations, we
do not find that the ’439 patent discloses such structure
corresponding to the “mechanism for managing” function.
Parts of the ’439 patent specification mention that the
linked and mirrored pair of file systems are “under the
management of MFS,” e.g., col. 9 ll. 56–57, col. 10, l. 14,
col. 11 l. 18, col. 12 ll. 35–37; however, the ’439 patent
does not describe the “managing” function as the two-step
process proposed by Twin Peaks.
    Therefore we must consider Twin Peaks’s further ar-
gument regarding the ’439 patent’s discussions of the
“mfs_open” operation and other file operations.     We
conclude that those disclosures also do not adequately
indicate what structure corresponds to the “mechanism
for managing” limitation. Referring to the code for the
“mfs_open” operation and the instructions to implement
TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION                15



other operations likewise, Twin Peaks contends that a
person of ordinary skill in the art would understand and
could implement other file operations by merely replacing
operation names and using known arguments of known
file operations.
     Similarly to claim 1, Twin Peaks relies on our case
law to suggest that as long as a structure sufficient for
one skilled in the art is disclosed, i.e., “critical” or “essen-
tial” structure, a structure to perform the entirety of the
function need not be disclosed to satisfy the definiteness
requirement for a means-plus-function claim. Appellant’s
Br. 10 (citing Creo Prods., Inc. v. Presstek, Inc., 305 F.3d
1337, 1347 (Fed. Cir. 2002); Cardiac Pacemakers, Inc. v.
St. Jude Med., Inc., 296 F.3d 1106, 1119 (Fed. Cir. 2002)).
Emphasizing the “interrelationship” between enablement
and definiteness from a skilled artisan’s perspective, Twin
Peaks asserts that “[l]ogically, if one skilled in the art can
build the invention and make it work, the scope of the
invention must be understood as well,” and that such logic
“necessarily follows from the test applied to determine
definiteness.” Id. at 14–15 (citing Atmel, 198 F.3d at
1382). Twin Peaks’s allegedly “logical” extrapolation,
however, is misplaced.
    “[T]he quid pro quo for the convenience of employing
§ 112, ¶ 6” is to clearly link or associate corresponding
structure to the claimed function. B. Braun Med., Inc. v.
Abbott Labs., 124 F.3d 1419, 1424 (Fed. Cir. 1997). The
“corresponding structure need not include all things
necessary to enable the claimed invention to work,”
Cardiac Pacemakers, 296 F.3d at 1119, because enable-
ment is a separate inquiry, and by engaging in functional
claiming under § 112 ¶ 6, a patentee is entering into the
bargain of limiting its open-ended functional claim term
to what is disclosed and their equivalents, which may not
be coextensive with the full enabled scope, see, e.g., B.
Braun Med., 124 F.3d at 1425 (limiting the scope of the
means-plus-function limitation in question to what is
16            TWIN PEAKS SOFTWARE INC.   v. IBM CORPORATION



disclosed in the specification). Indeed, Twin Peaks does
not appear to argue that the scope of the “mechanism for
managing” is limited to the “managing” function only
having the “open” operation and other file operations that
are considered its equivalents. Instead, Twin Peaks urges
that, because a person of ordinary skill in the art would
be able to understand other operations and implement
them “follow[ing] the same procedure,” the structure
corresponding to the full scope of the “managing” function
is disclosed. We decline to adopt such reasoning.
    As discussed above, the ’439 specification does not de-
scribe the “mechanism for managing” limitation as the
two-step process proposed by Twin Peaks. Furthermore,
as the district court noted, disclosure of the “open” opera-
tion is only a partial and inadequate disclosure of the file
operations that constitute the alleged full scope of the
“managing” function. We therefore conclude that the
“mechanism for managing” limitation of claim 4 is indefi-
nite and that the district court did not err in its conclu-
sion.
    Because we agree that the district court did not err in
concluding that the two means-plus-function claims
limitations are not supported by adequate structure in the
specification, we also agree that the court did not err in
concluding the challenged claims to be indefinite and
hence invalid.
                       CONCLUSION
    We have considered the remaining arguments, but
find them unpersuasive. For the foregoing reasons, the
decision of the district court is affirmed.
                       AFFIRMED
