  United States Court of Appeals
      for the Federal Circuit
                ______________________

 ADVANCED GROUND INFORMATION SYSTEMS,
                   INC.,
            Plaintiff-Appellant

                           v.

                   LIFE360, INC.,
                  Defendant-Appellee
                ______________________

                      2015-1732
                ______________________

   Appeal from the United States District Court for the
Southern District of Florida in No. 9:14-cv-80651-DMM,
Judge Donald M. Middlebrooks.
                ______________________

                Decided: July 28, 2016
                ______________________

    GEORGE BADENOCH, Kenyon & Kenyon LLP, New
York, NY, argued for plaintiff-appellant. Also represent-
ed by MARK ALEXANDER CHAPMAN, ROSE CORDERO PREY,
ALESSANDRA MESSING.

   DANIEL H. BREAN, The Webb Law Firm, Pittsburgh,
PA, argued for defendant-appellee. Also represented by
KENT E. BALDAUF, JR., BRYAN P. CLARK, CHRISTIAN D.
EHRET.
                ______________________
2               ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



    Before MOORE, MAYER, and WALLACH, Circuit Judges.
WALLACH, Circuit Judge.
    Advanced Ground Information Systems, Inc. (“AGIS”)
appeals the decision of the United States District Court
for the Southern District of Florida in Advanced Ground
Information Systems, Inc. v. Life360, Inc., No. 14-cv-80651
(S.D. Fla. Nov. 21, 2014) (J.A. 2–37), which found that
claims 3 and 10 of U.S. Patent No. 7,031,728 (“the ’728
patent”) and claims 5 and 9 of U.S. Patent No. 7,672,681
(“the ’681 patent”) (together, the “patents-in-suit”) invoke
35 U.S.C. § 112, ¶ 6, and that the claims are indefinite
under 35 U.S.C. § 112, ¶ 2 (2006). 1 Although the district
court found these claims indefinite, it did not address the
issue of invalidity because Appellee, Life360, Inc.,
(“Life360”) did not request a finding of invalidity. The
parties subsequently stipulated that these claims were
invalid for indefiniteness, see J.A. 857, and the court
entered its Final Judgment on May 12, 2015, see J.A. 1.
For the reasons articulated below, we affirm the district
court’s decision that the claims are indefinite, and accord-
ingly conclude that the asserted claims are invalid.
                       BACKGROUND
    AGIS is a technology company, software developer,
and military contractor, as well as the owner of the pa-
tents-in-suit. While the specifications of the patents-in-
suit differ from one another, the patents-in-suit relate to
methods, devices, and systems for establishing a commu-
nication network for users (referred to as “participants” in


     1  Congress amended 35 U.S.C. § 112 when it passed
the Leahy–Smith America Invents Act (“AIA”), and the
amendments took effect on September 16, 2012. Pub. L.
No. 112–29, § 4 125 Stat. 284, 296–97 (2011). Because the
applications resulting in the patents-in-suit were filed
before that date, we refer to the pre-AIA version of § 112.
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.     3



the patents-in-suit) of mobile devices, such as cellular
phones.
                    I. The Patents-in-Suit
                      A. The ’728 Patent
    The ’728 patent describes a cellular communication
system that allows multiple cellular phone users to moni-
tor others’ locations and statuses via visual display of
such information on a map. ’728 patent, Abstract. For
example, as illustrated in Figure 1 of the ’728 patent,
users of a mobile device can see the locations of other
users on the network (indicated by triangle 30 and square
34 symbols):




Id. fig.1. Symbols generated on the users’ cellular phones
represent the latitude and longitude of other users. Id.
col. 3 ll. 35–40. Users in the communication network may
initiate a phone call, send text messages, or send data or
4               ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



pictures with other users on the network by touching a
symbol representative of the other users on the screen.
Id. col. 11 ll. 12–13, 38–42.
                    B. The ’681 Patent
    The ’681 patent is a continuation-in-part of the ’728
patent. It describes how “a designated administrator
using a personal computer (PC) or other input device can
reprogram all user and network participants’ cell phone
devices to change, modify[,] or create new virtual switch
names and new symbols for a different operating envi-
ronment.” ’681 patent col. 2 ll. 3–7.
                 C. The Asserted Claims
    Claims 3 and 10 of the ’728 patent and claims 5 and 9
of the ’681 patent (collectively, the “asserted claims”)
recite a “symbol generator” that generates symbols repre-
senting each user in the network on the display of a user’s
cellular phone. Claim 3 of the ’728 patent is a system
claim that recites a “symbol generator in [a central pro-
cessing unit (‘CPU’)] that can generate symbols that
represent each of the participants’ cell phones in the
communication network on the display screen.” ’728
patent col. 12 ll. 62–64 (emphasis added). Claim 5 of the
’681 patent is a system claim similar to claim 3 of the ’728
patent in all relevant respects, except that it recites a
“symbol generator in [a] CPU that can generate symbols
that represent each of the participants in the communica-
tion network on the display screen,” ’681 patent col. 12 ll.
62–64 (emphasis added), as opposed to “each of the partic-
ipants’ cell phones,” ’728 patent col. 12 l. 63.
    Claim 10 of the ’728 patent and claim 9 of the ’681 pa-
tent are apparatus claims that recite a “cellular phone for
use in a communication network for a plurality of partici-
pants comprising . . . a symbol generator connected to [a]
CPU and [a] database for generating symbols on [a] touch
screen display screen.” ’728 patent col. 14 ll. 28–47 (em-
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.         5



phasis added); ’681 patent col. 13 l. 44–col. 14 l. 8 (same
(emphasis added)). Both claims also recite that the
cellular phone comprises “CPU Software.” See ’728 patent
col. 14 ll. 48–49 (stating that the cellular phone comprises
“CPU software for selectively polling other participants
with a cellular phone”); ’681 patent col. 14 ll. 9–10 (stating
that the cellular phone comprises “CPU software that
causes the exchange of data with other participants with
a cellular phone”).
                    II. Procedural History
    Life360 is a startup company and the creator of a
smartphone software application (the “Life360 mobile
app”). J.A. 2382. The Life360 mobile app was designed to
allow families to stay better connected––it “runs on [a]
mobile device to allow [users] to view [their] family mem-
bers on a map, communicate with them, and receive alerts
when [their] loved ones arrive at home, school[,] or work.”
Product Tour, https://www.life360.com/tour/ (last visited
July 26, 2016). On May 16, 2014, AGIS filed a complaint
in the district court alleging that the Life360 mobile app
infringed claims 3, 7, and 10 of the ’728 patent and claims
1, 5, and 9 of the ’681 patent. See J.A. 2–3.
    In response to AGIS’s Complaint, Life360 asserted
that the claim terms “symbol generator” and “CPU soft-
ware” in the asserted claims invoked means-plus-function
claiming allowed under 35 U.S.C. § 112, ¶ 6, but the
terms failed to disclose adequate structure and, therefore,
are indefinite under 35 U.S.C. § 112, ¶ 2. J.A. 262–70.
Paragraph 6 of 35 U.S.C. § 112 allows “[a]n element in a
claim for a combination” to “be expressed as a means or
step for performing a specified function without the
recital of structure, material, or acts in support thereof,
and such claim shall be construed to cover the correspond-
ing structure, material, or acts described in the specifica-
tion and equivalents thereof.” Pursuant to 35 U.S.C.
§ 112, ¶ 6, if the specification of a patent does not disclose
6                ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



“corresponding structure, material, or acts” for “perform-
ing the specified function” in the claims, the patent will be
found to be invalid for indefiniteness under 35 U.S.C.
§ 112, ¶ 2 because it does not “distinctly claim[] the
subject matter . . . the inventor . . . regards as the inven-
tion.” 35 U.S.C. § 112, ¶ 2.
    On November 21, 2014, the district court issued the
decision in dispute. See J.A. 2–37 (District Court’s
Markman Order). In addition to construing various
claims of the patents-in-suit, the district court found that
the terms “symbol generator” and “CPU software” in the
asserted claims––i.e., claims 3 and 10 of the ’728 patent
and claims 5 and 9 of the ’681 patent––invoked 35 U.S.C.
§ 112, ¶ 6, and were indefinite under 35 U.S.C. § 112, ¶ 2.
See J.A. 9–20. In view of the district court’s decision as to
indefiniteness, the parties stipulated that these claims
were invalid. See J.A. 857.
    AGIS appeals the district court’s indefiniteness de-
terminations. This court has jurisdiction over this appeal
under 28 U.S.C. § 1295(a)(1) (2012).
                        DISCUSSION
    Our analysis proceeds in two steps. First, we address
whether “symbol generator” in the asserted claims is in
means-plus-function form pursuant to 35 U.S.C. § 112,
¶ 6. See Robert Bosch, LLC v. Snap–On Inc., 769 F.3d
1094, 1097 (Fed. Cir. 2014). If we find that the relevant
claim terms recite a means-plus-function limitation, we
proceed to our second inquiry and “attempt to construe
the disputed claim term by identifying the corresponding
structure, material, or acts described in the specification
to which the term will be limited.” Id. (internal quotation
marks and citation omitted); see also O.I. Corp. v. Tekmar
Co., 115 F.3d 1576, 1583 (Fed. Cir. 1997) (“The price that
must be paid for use of [a means-plus-function claim] is
limitation of the claim to the means specified in the
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.        7



written description and equivalents thereof.”). However,
“[i]f the specification is not clear as to the structure that
the patentee intends to correspond to the claimed func-
tion, then the patentee has not paid that price but is . . .
attempting to claim in functional terms unbounded by
any reference to structure in the specification.” Med.
Instrumentation & Diagnostics Corp. v. Elekta AB, 344
F.3d 1205, 1211 (Fed. Cir. 2003). We address each step in
turn.
I. The Claim Term “Symbol Generator” Invokes 35 U.S.C.
                      § 112, ¶ 6
     The district court held that “symbol generator” and
“CPU software” in claims 3 and 10 of the ’728 patent and
claims 5 and 9 of the ’681 patent invoked 35 U.S.C. § 112,
¶ 6, but were indefinite under 35 U.S.C. § 112, ¶ 2.
“Symbol generator” appears in all of the asserted claims.
Thus, if we find that claim term indefinite under 35
U.S.C. § 112, ¶ 2, we need not independently address
whether the claim term “CPU software” also renders clam
10 of the ’728 patent and claim 9 of the ’681 patent invalid
for indefiniteness.
    The district court’s construction of patent claims
based on evidence intrinsic to the patent, including any
finding that the claim language invokes 35 U.S.C. § 112,
¶ 6, is reviewed de novo as a question of law. See Wil-
liamson v. Citrix Online, LLC, 792 F.3d 1339, 1346 (Fed.
Cir. 2015) (en banc) (citation omitted). In construing
patent claims, if the district court makes underlying
findings of fact based on extrinsic evidence, such findings
are reviewed for clear error. Id. “Clear error only exists if
we are left with a definite and firm conviction that a
mistake has been committed.” Venture Indus. Corp. v.
Autoliv ASP, Inc., 457 F.3d 1322, 1331 (Fed. Cir. 2006)
(internal quotation marks and citation omitted).
    If a claim element “contains the word ‘means’ and re-
cites a function,” this creates a presumption that the
8                ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



claim is in means-plus-function form under 35 U.S.C.
§ 112, ¶ 6. Envirco Corp. v. Clestra Cleanroom, Inc., 209
F.3d 1360, 1364 (Fed. Cir. 2000) (citation omitted). “That
presumption falls, however, if the claim itself recites
sufficient structure to perform the claimed function.” Id.
(citation omitted).
    “[T]he failure to use the word ‘means’ also creates a
rebuttable presumption—this time that § 112, para. 6
does not apply.” Williamson, 792 F.3d at 1348 (citation
omitted). However, “if the challenger demonstrates that
the claim term fails to recite sufficiently definite structure
or else recites function without reciting sufficient struc-
ture for performing that function,” this presumption may
be rebutted. Id. (internal quotation marks, brackets, and
citation omitted). “The standard is whether the words of
the claim are understood by persons of ordinary skill in
the art to have a sufficiently definite meaning as the
name for structure.” Id. at 1349. In determining whether
this presumption has been rebutted, the challenger must
establish by a preponderance of the evidence that the
claims are to be governed by § 112, ¶ 6. See Apex Inc. v.
Raritan Comput. Inc., 325 F.3d 1364, 1372 (Fed. Cir.
2003).
    Here, although the asserted claims do not include the
word “means,” the district court determined that AGIS
intended to invoke § 112, ¶ 6. See J.A. 10–11; see also
’728 patent col. 12 l. 52–col. 13 l. 13 (claim 3), col. 14 ll.
27–61 (claim 10); ’681 patent col. 12 l. 52–col. 13 l. 18
(claim 5), col. 13 l. 44–col. 14 l. 27 (claim 9). According to
the district court, “[a] plain reading of the term in context
of the relevant claim language suggests the term ‘symbol
generator’ is analogous to a ‘means for generating sym-
bols’ because the term is simply a description of the
function performed.” J.A. 10–11 (citation omitted). The
district court also determined “the term is not used in
common parlance or by persons of ordinary skill in the
pertinent art to designate structure.” J.A. 11 (internal
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.          9



quotation marks and citation omitted). Finally, the
district court rejected the testimony of AGIS’s expert, Dr.
Benjamin Goldberg, because he was “not aware whether
the term symbol generator has a meaning in computer
science.” J.A. 11 (internal quotation marks and citation
omitted).
    AGIS challenges the district court’s determination,
asserting that the district court “erred when it concluded
that the ‘symbol generator’ elements in [the asserted
claims] are subject to § 112, ¶ 6.” AGIS’s Br. 25. Specifi-
cally, AGIS avers that Life360 failed to present sufficient
evidence demonstrating that “symbol generator” invokes
§ 112, ¶ 6. See id. at 26, 32. According to AGIS, “[t]he
unrebutted expert evidence [of Dr. Goldberg] . . . showed
that persons of ordinary skill would have understood the
claimed symbol generator to have a sufficiently definite
meaning as the name for structure.” Id. at 26–27 (inter-
nal quotation marks and citation omitted); see also id. at
27 (stating that “Dr. Goldberg testified that those skilled
in the art would have understood a ‘symbol generator’ to
refer to a well-known class of existing, available, standard
modules of software code used to generate symbols on a
display” (citations omitted)).
     The term “symbol generator” invokes the application
of § 112, ¶ 6 because it fails to describe a sufficient struc-
ture and otherwise recites abstract elements “for” causing
actions, ’728 patent col. 14 ll. 45–47, or elements “that
can” perform functions, ’681 patent col. 12 l. 62. Through
the testimony of Dr. Goldberg, AGIS contends “those
skilled in the art would have understood a ‘symbol gener-
ator’ to refer to a class of structures instead of a particular
structure.” AGIS’s Br. 27; see also id. at 28 (stating that
“Dr. Goldberg’s unrebutted testimony that those skilled in
the art would have understood what a ‘symbol generator’
is, and would have known how to select and use one from
the well-known class of software modules, demonstrates
10              ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



that the words have a sufficiently definite meaning as the
name for structure” (internal quotation marks and cita-
tion omitted)). However, contrary to AGIS’s contention,
Dr. Goldberg testified that the term “symbol generator” is
a term coined for the purposes of the patents-in-suit. See
J.A. 798. The term is not used in “common parlance or by
persons of skill in the pertinent art to designate struc-
ture,” such that it connotes sufficient structure to avoid
the application of 35 U.S.C. § 112, ¶ 6. Lighting World,
Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1359
(Fed. Cir. 2004), overruled on other grounds by William-
son, 792 F.3d at 1348–49.
     We see no clear error in the district court’s findings
regarding Dr. Goldberg’s testimony.        Dr. Goldberg’s
testimony that the terms “symbol” and “generator” are
known within the field of computer science is not disposi-
tive and does not require us to find that 35 U.S.C. § 112,
¶ 6 does not apply. See J.A. 11 (stating that “Dr. Gold-
berg testified he was aware of the terms ‘symbol’ and
‘generator’ separately, but was unaware of [the] use [of]
the specific term ‘symbol generator’ within the field of
computer science” (citation omitted)). Irrespective of
whether the terms “symbol” and “generator” are terms of
art in computer science, the combination of the terms as
used in the context of the relevant claim language sug-
gests that it is simply an abstraction that describes the
function being performed (i.e., the generation of symbols).
See, e.g., ’728 patent col. 3 ll. 44–46 (“Each cellular
phone/[Personal Digital Assistant (‘PDA’)/[Global Posi-
tioning System (‘GPS’)]” is identified on the display of
other phone systems by a symbol that is generated to
indicate its identity.” (emphasis added)); see also ’681
patent col. 7 ll. 14–17 (“Each cellular phone device is
identified on the map display of the other participant/user
cell phone devices by a display symbol that is generated on
each user cell phone device display to indicate each user’s
identity.” (emphasis added)).
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.      11



    Finally, the claim term “symbol generator,” by itself,
does not identify a structure by its function, cf. Personal-
ized Media Commc’ns v. ITC, 161 F.3d 696, 705 (Fed. Cir.
1998) (stating that the claim term “digital detector” does
not invoke § 112, ¶ 6 because “[e]ven though the term
‘detector’ does not specifically evoke a particular struc-
ture, it does convey to one knowledgeable in the art a
variety of structures known as ‘detectors’”), nor do the
asserted claims suggest that the term “symbol generator”
connotes a definite structure, see Media Rights Techs.,
Inc. v. Capital One Fin. Corp., 800 F.3d 1366, 1372 (Fed.
Cir. 2015) (finding that the term “compliance mechanism”
invokes § 112, ¶ 6, because the asserted claims “simply
state that the ‘compliance mechanism’ can perform vari-
ous functions” (emphasis added)). Accordingly, because
the term “symbol generator” does not describe anything
structural, the district court was correct to conclude that
the asserted claims which recite the term “symbol genera-
tor” are subject to 35 U.S.C. § 112, ¶ 6.
   II. The Claim Term “Symbol Generator” Is Indefinite
                    Under § 112, ¶ 2
    Because the claim term “symbol generator” is a
means-plus-function term as described by paragraph 6 of
§ 112, we must “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, 769 F.3d at 1097 (internal
quotation marks and citation omitted). If a patentee
“employs means-plus-function language in a claim, [the
patentee] must set forth in the specification an adequate
disclosure showing what is meant by that language.”
Blackboard, Inc. v. Desire2Learn, Inc., 574 F.3d 1371,
1382 (Fed. Cir. 2009) (internal quotation marks and
citation omitted). “If the specification does not contain an
adequate disclosure of the structure that corresponds to
the claimed function, the patentee will have failed to
particularly point out and distinctly claim the invention
12               ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.



[under § 112, ¶ 2], which renders the claim invalid for
indefiniteness.” Id. (internal quotation marks and cita-
tion omitted).
     We agree with the district court’s determination that
the “term ‘symbol generator’ is indefinite.” J.A. 13 (foot-
note omitted). Although the district court recognized that
“the specification [] describe[s], in general terms, that
symbols are generated based on the latitude and longi-
tude of the participants,” it nonetheless determined that
the specification “fails to [disclose] an ‘algorithm’ or
description as to how those symbols are actually ‘generat-
ed.’” J.A. 12 (citation omitted).
     “[I]n a means-plus-function claim in which the dis-
closed structure is a computer[] or microprocessor[] pro-
grammed to carry out an algorithm, [as is the case here],
the disclosed structure is . . . [a] special purpose comput-
er programmed to perform the disclosed algorithm.”
Aristocrat Techs. Austl. Pty Ltd. v. Int’l Game Tech., 521
F.3d 1328, 1333 (Fed. Cir. 2008) (internal quotation
marks and citation omitted); see ’728 patent col. 3 ll. 57–
61 (stating that “[w]hen the cellular phone/PDA/GPS
System user uses his stylus or finger to touch one or more
of the symbols or a location on the cellular phone display,
the system’s software causes the status and latitude and
longitude information concerning that symbol or location
to be displayed”). In the case of computer-implemented
functions, we require that the specification “disclose an
algorithm for performing the claimed function.” See Net
MoneyIN, Inc. v. VeriSign, Inc., 545 F.3d 1359, 1367 (Fed.
Cir. 2008). The specification can express the algorithm
“in any understandable terms including as a mathemati-
cal formula, in prose, . . . as a flow chart, or in any other
manner that provides sufficient structure.” Finisar Corp.
v. DirecTV Grp., Inc., 523 F.3d 1323, 1340 (Fed. Cir. 2008)
(citation omitted).
ADVANCED GROUND INFO. SYS., INC.   v. LIFE360, INC.    13



    The specifications of the patents-in-suit do not dis-
close an operative algorithm for the claim elements recit-
ing “symbol generator.”       The function of generating
symbols must be performed by some component of the
patents-in-suit; however, the patents-in-suit do not de-
scribe this component. Although the specification of the
’728 patent suggests that these symbols are generated via
“a map database and a database of geographically refer-
enced fixed locations . . . with a specified latitude and
longitude[,] . . . [and] [a] database with the constantly
updated GPS location,”’ 728 patent col. 3 ll. 35–41, this
only addresses the medium through which the symbols
are generated. A patentee cannot claim a means for
performing a specific function and subsequently disclose a
“general purpose computer as the structure designed to
perform that function” because this “amounts to pure
functional claiming.” Aristocrat Techs., 521 F.3d at 1333.
Accordingly, because the specifications of the patents-in-
suit do not disclose sufficient structure for the “symbol
generator” function and the asserted claims include this
term, the asserted claims are indefinite under 35 U.S.C. §
112, ¶ 2.
                         CONCLUSION
    For the foregoing reasons, the decision of the United
States District Court for the Southern District of Florida
is
                         AFFIRMED
