       NOTE: This disposition is nonprecedential.


  United States Court of Appeals
      for the Federal Circuit
                 ______________________

     MIRROR WORLDS TECHNOLOGIES, LLC,
              Plaintiff-Appellant

                            v.

                   FACEBOOK, INC.,
                   Defendant-Appellee
                 ______________________

                       2018-2276
                 ______________________

   Appeal from the United States District Court for the
Southern District of New York in No. 1:17-cv-03473-JGK,
Judge John G. Koeltl.
                 ______________________

                Decided: January 23, 2020
                 ______________________

    MARC AARON FENSTER, Russ August & Kabat, Los An-
geles, CA, argued for plaintiff-appellant. Also represented
by BRIAN DAVID LEDAHL, JAMES S. TSUEI, BENJAMIN T.
WANG; CHARLES R. MACEDO, Amster Rothstein &
Ebenstein LLP, New York, NY.

    HEIDI LYN KEEFE, Cooley LLP, Palo Alto, CA, argued
for defendant-appellee. Also represented by DENA CHEN,
LOWELL D. MEAD, MARK R. WEINSTEIN; PHILLIP EDWARD
MORTON, Washington, DC.
2             MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




                   ______________________

    Before PROST, Chief Judge, TARANTO and STOLL, Circuit
                           Judges.
TARANTO, Circuit Judge.
    Mirror Worlds Technologies, LLC owns U.S. Patent
Nos. 6,006,227, 7,865,538, and 8,255,439, which describe
and claim systems and methods for presenting and storing
data in time-ordered streams on a computer system. Mir-
ror Worlds brought the present action against Facebook,
Inc., alleging that Facebook’s making, selling, using, and
other actions involving various Facebook systems infringed
the ’227, ’538, and ’439 patents. Facebook filed a motion
for summary judgment of non-infringement before discov-
ery ended, and the district court granted it. Mirror Worlds
appeals.
    We agree with Mirror Worlds that the district court’s
judgment must be reversed. The district court relied for its
decision on an erroneous conclusion that there is no genu-
ine dispute about certain facts. Facebook defends the sum-
mary judgment on alternative grounds. We will not affirm
on those alternative grounds. We reverse the court’s judg-
ment and remand for further proceedings.
                              I
                             A
    The ’227 patent issued from an application filed in June
1996. The ’538 and ’439 patents are descendants of the ’227
patent through a series of continuation applications, with
an intervening continuation-in-part application. The ’227
patent is representative for the purposes of this appeal.
    The patent states that, as of its priority date, conven-
tional computers used certain kinds of hierarchical directo-
ries to store and organize data. ’227 patent, col. 1, lines
21–30. Under the conventional system, a user created a
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.                 3



new document by naming the document and choosing a
storage location. Id. According to the patent, requiring
such operations has disadvantages: specifically, the opera-
tions involve needless overhead; file names are often mean-
ingless to a user; and a user of such a system must
remember not just the file name but where the document
is stored. Id., col. 1, lines 40–59. The ’227 patent describes
an alternative: storing documents in a chronologically or-
dered “stream.” Id., col. 1, lines 4–6.
     A “stream” is “a time-ordered sequence of documents
that functions as a diary of a person or an entity’s electronic
life. Every document created and every document sen[t] to
a person or entity is stored in a main stream.” Id., col. 4,
lines 6–10. Past documents are contained in the tail of the
stream, id., col. 4, lines 10–12, and new documents are
added to the present time point in the stream, id., col. 4,
lines 35–43. Besides containing documents from the past
and present, a stream may contain “documents allotted to
future times and events, such as[] reminders, calendar
items, and to-do lists.” Id., col. 4, lines 18–21. “A document
can contain any type of data,” including “pictures, corre-
spondence, bills, movies, voice mail and software pro-
grams.” Id., col. 4, lines 16–18.
    A user may create “substreams” by filtering the main
stream. Id., col. 4, lines 48–61. Describing preferred em-
bodiments, the patent characterizes a substream as dy-
namic and persistent in the following sense: if a user filters
for “all emails from Smith,” a substream containing all
emails from Smith will collect any such emails as they are
added to the main stream, and the substream will continue
to exist “until destroyed by the user.” Id., col. 4, line 62,
through col. 5, line 13. A substream is a subset of the main
stream, in that each substream document is in the main
stream, though a particular document may be in multiple
substreams. Id., col. 5, lines 14–19.
4            MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




   Claim 13 of the ’227 patent is representative for the is-
sues on appeal:
    13. A method which organizes each data unit re-
        ceived by or generated by a computer system,
        comprising the steps of:
    generating a main stream of data units and at least
       one substream, the main stream for receiving
       each data unit received by or generated by the
       computer system, and each substream for con-
       taining data units only from the main stream;
    receiving data units from other computer systems;
    generating data units in the computer system;
    selecting a timestamp to identify each data unit;
    associating each data unit with at least one chron-
        ological indicator having the respective
        timestamp;
    including each data unit according to the
        timestamp in the respective chronological indi-
        cator in at least the main stream; and
    maintaining at least the main stream and the sub-
       streams as persistent streams.
Id., col. 16, lines 9–25. Each of the asserted claims contains
a “main stream” or “main collection” limitation and a “sub-
stream” or “subcollection” limitation.
    The parties agree that the “main stream” has two prop-
erties: first, it includes every data unit received or gener-
ated by the “computer system”; second, it is a time-ordered
sequence of data units. 1 While Facebook contends that



    1  The ’538 and ’439 patents use the term “docu-
ments” rather than “data units.” Although the parties
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.              5



“main stream”—used in the ’227 and ’538 patents—and
“main collection”—used in the ’439 patent—are synony-
mous, Mirror Worlds disagrees. Mirror Worlds admits,
however, that any difference is immaterial to the resolu-
tion of Facebook’s summary judgment motion.
                             B
     Facebook provides a popular social networking service.
Several features of Facebook’s service are relevant to this
appeal. According to Facebook’s description in this case,
the “News Feed” for a Facebook user displays a variety of
items that Facebook has “deemed to be relevant” to that
user. J.A. 1104. “Timeline,” Facebook says, “focuse[s] on a
particular Facebook user,” showing “basic information
about that user, as well as actions taken on Facebook by or
directed toward that user.” Id. And “Activity Log” provides
“a list of activities that occurred on Facebook that pertain
to a particular user.” J.A. 1106. 2
    Generally, the content Facebook users see is an amal-
gamation of “objects” and “associations,” which are two
classes of data. Users, pictures, and comments are types of
objects, while associations describe the relationship be-
tween objects. For example, if user “Alice” posts a comment
on Facebook, an “authorship” association would connect Al-
ice and the comment.
    In providing content to users, both News Feed and
Timeline rely on certain “front-end” hardware and soft-
ware. The evidence—when understood most favorably to
Mirror Worlds, as required when considering summary
judgment—indicates that these front-end components


disagree about whether those terms are synonymous, any
difference is immaterial to our decision in this appeal.
    2   At least two of the three patents at issue here have
expired. Nevertheless, following the parties’ usage, we use
the present tense in describing the accused services.
6           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




include a user’s desktop computer, smartphone, or compa-
rable device and its resident software, together with cer-
tain “web” technologies, including a PHP layer. See, e.g.,
J.A. 1483–85, 1488, 1550, 2117–18, 2132, 2422, 2599. The
two services also rely on certain “back-end” computing
equipment and associated software to which the user’s de-
vice is connected over a network such as the Internet. The
back-end infrastructure for News Feed is called “Mul-
tifeed.” The “Timeline back-end system” supports both the
Timeline and Activity Log features. In the summary-judg-
ment proceedings, Mirror Worlds asserted that those two
back-end systems were the “computer system[s]” for pur-
poses of the claims.
     Multifeed has several components, of which three have
been featured in this appeal: Leaves, Tailer, and Aggrega-
tor. 3 Facebook describes Leaves as a collection of data-
bases of information about user actions and objects. Tailer,
in turn, writes user actions and objects to Leaves. Aggre-
gator retrieves information from Leaves and applies an ag-
gregation algorithm to create a list of stories that may be
shown on a particular user’s News Feed.
     The Timeline back-end system includes the Time-
lineDB database and an Aggregator. TimelineDB has a list
of all actions performed by a user. Similar to the Multifeed
Aggregator, the Timeline Aggregator serves as an interme-
diary between the front end and the database. When a user
views Timeline, the front end passes parameters to the
Timeline Aggregator, which then retrieves information



    3    For simplicity, and to maintain parallelism with
the other relevant components, we will refer to “Leaves” in
the singular as a unit, though the evidence sometimes re-
fers to “the Leaves” in the plural. The parties have not
identified any way in which such treatment alters the anal-
ysis relevant to our decision.
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.               7



from TimelineDB that is used to create (or render) the im-
age on the user’s screen.
    Neither Multifeed nor the Timeline back-end system
contains all the information necessary to produce the fea-
tures they support. The News Feed and Timeline features
rely in part on another Facebook system known as “TAO,”
which stands for “The Associations and Objects.” Facebook
describes TAO as a “data store that provides access to ob-
jects and their associations with other objects.” J.A. 1111.
Retrieving objects such as photographs or comments to dis-
play on a user’s News Feed or Timeline uses, respectively,
Multifeed Leaves or TimelineDB, but those back-end com-
ponents contain pointers to the objects, not the objects
themselves. It is TAO that is called on to deliver up-to-date
versions of the objects to which Leaves and TimelineDB
point. Those objects then become part of the News Feed or
Timeline viewed by the user.
                             C
    In May 2017, Mirror Worlds filed this action against
Facebook in the District Court for the Southern District of
New York, alleging that Facebook infringed the asserted
patents by, e.g., using its servers—including TAO—to pro-
vide features such as News Feed, Timeline, and Activity
Log to Facebook users. In its first set of interrogatories,
Facebook asked Mirror Worlds to identify what elements of
the accused Facebook services that it was alleging meet the
“main stream” and “substream” limitations. J.A. 2472–73.
Facebook did not ask Mirror Worlds to identify what “com-
puter system[s]” it was accusing. Id. Mirror Worlds re-
sponded in early December 2017. J.A. 2473. Mirror Worlds
identified, as meeting the “main stream” limitation, “the
user-related information in at least Facebook’s Social
Graph, MemCache, TAO, Multifeed Leaf Servers and Ag-
gregators, Timeline Databases and Aggregators, Channel
Servers and RTGW Messaging Bus, and servers, databases
or aggregators from which Facebook’s Events, Activity Log,
8            MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




Graph Search, and search features obtain information for
Facebook users.” J.A. 2473. Mirror Worlds identified, as
meeting the “substream” limitation, “the user-related in-
formation that appears in at least Facebook’s Newsfeed,
Timeline, Events, Activity Log, Graph Search, and search
features.” J.A. 2473.
    Fact discovery was not due to close until September
2018. See J.A. 1045–46, 1057, 1061. But in April 2018,
after completion of the briefing on claim construction—but
before significant expert or other factual discovery had oc-
curred—Facebook filed a letter with the court, asking per-
mission to file a motion for summary judgment. J.A. 1015–
17. At a status conference, Facebook argued that it had a
simple, case-ending point to make, while Mirror Worlds as-
serted that contention interrogatories cannot be filed under
local rules until the close of fact discovery, that it was not
accusing Facebook as a whole but had identified the two
back-end systems separately from TAO, and that the rec-
ord did not even include expert disclosures or depositions.
The court granted Facebook leave to file a motion for sum-
mary judgment and set out a schedule for responses, while
allowing discovery to continue. J.A. 1065–66.
    In its motion for summary judgment of non-infringe-
ment, Facebook made essentially just one point. See
J.A. 1095–97. It contended that Mirror Worlds had failed
to provide evidence that there was an accused Facebook
“computer system” that contained a “main stream” in
which all data created or received by the system is stored
in a time-ordered sequence. In support of that contention,
Facebook argued, simply, that Mirror Worlds had included
TAO in the accused “computer system[s],” J.A. 1087–89,
and that the evidence established that “TAO does not store
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.               9



all of its data items in any kind of time-ordered sequence,”
J.A. 1095. 4
     In response, Mirror Worlds explained principally that
Facebook’s motion misunderstood what the accused “com-
puter system[s]” were. Specifically, it argued that it is the
News Feed back-end system, Multifeed, and the Timeline
back-end system specifically that are the systems accused
of coming within the asserted patent claims. See, e.g.,
J.A. 1422 (“[t]he Multifeed and Timeline backend sys-
tems”), 1439 (“the Multifeed system”), 1440 (“the Timeline
backend system”). Mirror Worlds contended that within
the Multifeed system, Leaves meets the “main stream” lim-
itation, and that within the Timeline system, TimelineDB
meets the limitation. See, e.g., J.A. 1421, 1438–40. Accord-
ing to Mirror Worlds, both Leaves and TimelineDB include
every data unit received by their respective computer sys-
tem and store those data units in a time-ordered sequence.
J.A. 1438–40 (asserting inclusion of “every data unit”); see
J.A. 1421, 1427, 1434, 1436, 1439, 1440 (asserting inclu-
sion of every action and object in the respective systems,
citing evidence). It does not matter how TAO stores its
data, Mirror Worlds argued, because TAO is separate from
Multifeed and the Timeline back-end system. J.A. 1421–
22.
     In reply, Facebook argued that Mirror Worlds had
failed to identify the relevant “computer system[s]” to
which Leaves and TimelineDB belong. J.A. 2508–09. Fa-
cebook emphasized that both Leaves and TimelineDB con-
sist primarily of pointers used to find corresponding data
in TAO and that News Feed and Timeline as seen by users


    4   Facebook mentioned, as a descriptive matter, that
the substream and sub-collection data must be drawn from
the main stream and main collection, but it made no sepa-
rate argument that evidence was missing as to the sub-
stream/sub-collection limitations. J.A. 1095–97.
10           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




include data from TAO. J.A. 2509–11. In a footnote, Face-
book cited certain evidence as assertedly showing that, in
the Multifeed system, the Aggregator “retrieve[s] data
units from the non-accused TAO data store.” J.A. 2508–
09 n.4. On those bases, Facebook contended, Leaves and
TimelineDB cannot meet the “main stream” limitation.
J.A. 2511–12. Facebook did not dispute that Leaves and
TimelineDB store their data units in a time-ordered man-
ner. 5
    The court allowed Mirror Worlds to file a surreply. In
that filing, Mirror Worlds reiterated its contentions that
Multifeed and the Timeline back-end system were the rel-
evant “computer system[s],” and Leaves and TimelineDB
met the “every data unit” requirement for being “main
streams” for those systems, even if information from other
systems might be necessary to create the News Feed and
Timeline features seen by users. J.A. 2675–77. It also as-
serted that, contrary to Facebook’s footnote suggestion, the
evidence showed that the Aggregators do not receive the
TAO data at issue, which, rather, is obtained by the (unac-
cused) front-end PHP feature. J.A. 2676 n.4 (citing
J.A. 2604, 2610 (also appearing at 2430)).
    When it granted Mirror Worlds leave to file a surreply,
the district court instructed Facebook that it should “resist
the urge to file further papers in response to Mirror
Worlds’[] sur reply brief.” J.A. 2673. Instead, the court as-
sured the parties that it would “consider all of the argu-
ments raised . . . at oral argument.” Id. At the oral
argument, Facebook argued that Mirror Worlds still failed
to show that the Facebook systems meet the “main stream”
limitation. One of its arguments—the one originally sug-
gested in its Reply footnote (discussed above)—was that


     5  Facebook added a new argument about Mirror
Worlds’ failure to show that the “substream” and “sub-col-
lection” limitations are met. J.A. 2512–13.
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.             11



the Aggregators receive data from TAO, not just Time-
lineDB or Leaves. Facebook also argued that the Aggrega-
tors receive data from certain sources that Facebook had
never mentioned until the oral argument. J.A. 60–61, 119–
20.
    The district court granted Facebook’s motion for sum-
mary judgment on August 11, 2018. The court determined
that the record established conclusively—so that there was
no genuine issue of fact about the proposition—that neither
TimelineDB nor Leaves (which Mirror Worlds identified as
the accused main streams) contains all the data received or
generated by their respective computer system. The court
reasoned that the Aggregators are parts of the accused
“computer system[s]” and concluded that it was beyond
reasonable dispute on this record that the Aggregators
(hence the systems) receive data from TAO that does not
enter TimelineDB or Leaves. Because there is data re-
ceived by the accused systems that is not included in Time-
lineDB or Leaves, the court held, TimelineDB and Leaves
cannot be main streams. Mirror Worlds Technologies, LLC
v. Facebook, Inc., 320 F. Supp. 3d 538, 547 (S.D.N.Y. 2018).
    The court entered judgment on August 16, 2018. Mir-
ror Worlds timely appealed. We have jurisdiction under 28
U.S.C. § 1295(a)(1).
                             II
    We review a “grant of summary judgment of non-in-
fringement under the law of the relevant regional circuit.”
Clare v. Chrysler Grp., 819 F.3d 1323, 1326 (Fed. Cir.
2016). The Second Circuit reviews a grant of summary
judgment de novo. Rojas v. Roman Catholic Diocese of
Rochester, 660 F.3d 98, 104 (2d Cir. 2011). “The court shall
grant summary judgment if the movant shows that there
is no genuine dispute as to any material fact and the mo-
vant is entitled to judgment as a matter of law.” Fed. R.
Civ. P. 56(a). “[S]ummary judgment will not lie if the dis-
pute about a material fact is ‘genuine,’ that is, if the
12           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




evidence is such that a reasonable jury could return a ver-
dict for the nonmoving party.” Anderson v. Liberty Lobby,
Inc., 477 U.S. 242, 249 (1986). When determining whether
summary judgment is appropriate, a court must resolve all
ambiguities and draw all reasonable inferences against the
moving party. Matsushita Electrical Industrial Co. v. Zen-
ith Radio Corp., 475 U.S. 574, 587 (1986).
                             A
    The district court rested its summary-judgment ruling
on a single basis—its determination that one fact could rea-
sonably be found only in Facebook’s favor. Mirror Worlds
challenges that determination. Specifically, Mirror Worlds
argues that the district court erred in concluding that the
record would require a reasonable jury to find that the Ag-
gregators in Multifeed and in the Timeline back-end sys-
tem receive data from TAO—data that is not included
within Leaves or TimelineDB. We agree that the district
court erred in so concluding.
                             1
     Regarding News Feed and its back-end system, Mul-
tifeed, the district court concluded that the record required
a finding that the Aggregator “draws the actual content
that is indexed by the ‘Multifeed Leaves’ from ‘TAO,’ and
receives information from ‘TAO.’” Mirror Worlds, 320 F.
Supp. 3d at 546. The court relied on a declaration of
Dr. Bronson, a Facebook engineer, and the testimony of
Dr. Vickery, another Facebook engineer. Id. But that evi-
dence does not establish that the Multifeed Aggregator re-
ceives content from TAO that is not in Leaves.
     The Bronson declaration states that “when News Feed,
Timeline, [and] Activity Log . . . seek to retrieve objects
such as photos and comments from Facebook’s data store,
it is TAO that retrieves and delivers an up-to-date version
of those objects to those features.” J.A. 1111–12 (emphasis
added). The quoted statement does not say that TAO
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.              13



delivers content to the Multifeed Aggregator (in the back-
end system). It states only that the content is delivered to
the front-end features, including News Feed. The state-
ment is consistent with Mirror Worlds’ theory of the case,
and it does not establish that the identified data from TAO
is received by the accused “computer system” (the back-end
system), which is the premise of the district court’s deter-
mination that Leaves, in the back-end system, cannot be a
main stream (because that TAO data is not included in
Leaves).
    A similar conclusion is required as to Dr. Vickery’s tes-
timony. Dr. Vickery said that “the aggregators combine to-
gether metadata that’s received from the leaves into
another list of metadata that has several steps such as que-
rying TAO . . . to fetch additional information that is re-
quired to render someone’s News Feed.” J.A. 2595. Dr.
Vickery also said that “one of the most important things in
generating someone’s News Feed is their list of friends and
the pages that they follow. And that information is queried
from TAO.” J.A. 2599. Those statements, like Dr. Bron-
son’s statement discussed above, do not establish that the
referred-to data from TAO enters the Aggregator or, there-
fore, the only accused system for News Feed, i.e., Multifeed.
     In another statement, Dr. Vickery said that the
“[a]ggregators combine together information from mul-
tifeed leaf servers as well as other sources in order for—as
the next step in preparing someone’s News Feed.”
J.A. 2595 (emphasis added). But that testimony does not
clearly state that the Multifeed Aggregator retrieves the
cited information from TAO. It is not enough to remove the
issue from genuine dispute, especially in the face of evi-
dence suggesting otherwise. See, e.g., J.A. 2014 (Face-
book’s Dr. Bronson indicating it is the “application layer”
that “queries TAO using [the] backend identifiers”), 2030
(Dr. Bronson discussing certain “trace” tests: “My recollec-
tion is that all the TAO queries that—that were initiated
14           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




as, like, directly in response to rendering my News Feed
came from the—the PHP application layer.”).
     In fact, other testimony from Dr. Vickery suggests that
TAO is queried by a part of the front-end system called the
PHP layer (PHP being a scripting language). For example,
Dr. Vickery testified that “the list of story identifiers that
the aggregator returns back to PHP contains pointers
which can be used, perhaps through a series of steps, to
fetch the set of information that will be rendered in the fi-
nal story” and the returned list of story identifiers “deter-
mines what queries to TAO will be run in order to generate
those stories.” J.A. 2604. Additional testimony of Dr. Vick-
ery further suggests that the PHP layer, not the Aggrega-
tor, queries TAO. J.A. 2602–04.
    We conclude that, on the current record evidence, the
district court erred in concluding that a reasonable jury
would have to find that the Multifeed Aggregator receives
data from TAO that is not in Leaves. That erroneous con-
clusion was the sole basis for the grant of summary judg-
ment as to News Feed.
                              2
    Our conclusion regarding Timeline is similar to our
conclusion regarding News Feed. The district court con-
cluded that a reasonable jury would have to find that the
Timeline Aggregator receives data from TAO that is not in
TimelineDB. Mirror Worlds, 320 F. Supp. 3d at 546–47.
The court cited the declaration of Dr. Bronson; Mirror
Worlds’ response to Facebook’s statement of material facts;
and the testimony of Jeffrey Huang, a Facebook engineer.
Id. at 546. We conclude, to the contrary, that the record
evidence, as presented to the district court and identified
to us, does not compel a reasonable jury to find that the
Timeline Aggregator receives the asserted data from TAO.
    As for Dr. Bronson, the district court relied on the
statement by Dr. Bronson we addressed above in
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.            15



discussing the News Feed aspect of the case. As discussed,
Dr. Bronson’s statement does not show that the Timeline
Aggregator receives the cited data from TAO.
    Mirror Worlds’ response to Facebook’s statement of
material facts also does not show, as Facebook contends,
that the Timeline Aggregator receives the relevant data
from TAO. In the paragraphs cited by the court, Mirror
Worlds discussed only querying of the TimelineDB, not of
TAO, by the Timeline Aggregator. J.A. 1464–67. Facebook
has not pointed to anything in the Mirror Worlds’ response
that supports the district court’s crucial determination
about interaction between the Timeline Aggregator and
TAO.
    Mr. Huang’s testimony is similarly insufficient. Mr.
Huang testified that “[i]n order to actually show anything
on Timeline, you need to take those IDs you get from the
TimelineDB and go to TAO to actually fetch the content.”
J.A. 2587. Like Dr. Bronson’s testimony, Mr. Huang’s tes-
timony does not show that the Timeline Aggregator is the
element of Facebook’s infrastructure that receives the re-
ferred-to content from TAO. Mr. Huang’s testimony is con-
sistent with the theory that front-end systems receive that
content without the content having first gone through the
accused (back-end) system. Indeed, other testimony by Mr.
Huang suggests that the front-end web layer retrieves that
content: Mr. Huang testified that “it’s really the web tier
that I consider the frontend that then, you know, needs to
go to TAO to actually fetch any of the content.” J.A. 1910–
11. At least one internal Facebook document corroborates
Mr. Huang’s testimony that the front end, including PHP,
queries TAO. J.A. 2430.
    We conclude that, on the current record evidence, the
district court erred in concluding that a reasonable jury
would have to find that the Timeline Aggregator receives
data from TAO that is not in TimelineDB. That erroneous
16           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




conclusion was the sole basis for the grant of summary
judgment as to Timeline.
                               B
   Facebook asks us to affirm on grounds other than the
ones relied on by the district court. We find neither of its
two arguments to be a sound basis for affirmance here.
     First, citing Celotex Corp. v. Catrett, 477 U.S. 317
(1986), Facebook argues that it is entitled to summary
judgment under Federal Rule of Civil Procedure 56 on the
ground that Mirror Worlds failed to provide evidence that
would permit a jury to find that Leaves or TimelineDB con-
tains every data unit received or generated by, respectively,
Multifeed or the Timeline back-end system. The Second
Circuit has explained that “when a defendant moves for
summary judgment, it is the defendant who must show en-
titlement to judgment, notwithstanding that, at trial, the
plaintiff will have the burden of proving every element of
its claim.” Nick’s Garage, Inc. v. Progressive Casualty Ins.
Co., 875 F.3d 107, 115 (2d Cir. 2017). “The mere assertion
by a defendant moving for summary judgment that the
plaintiff ‘has not produced any evidence’ to support an es-
sential element of the plaintiff’s claim does not satisfy the
burden that Rule 56(a) imposes.” Id. “[U]nless the moving
defendant cites portions of the record that show its entitle-
ment to judgment, an assertion by the defendant that the
plaintiff ‘has not produced any evidence,’ without more,
does not show that the plaintiff has insufficient evidence.”
Id. at 115–16.
    Facebook, in its summary-judgment motion, did not
show that Mirror Worlds “cannot produce admissible evi-
dence to carry its burden” to show that Leaves or Time-
lineDB contains every data unit. Fed. R. Civ. P. 56(c)
advisory committee’s note to 2010 amendment. “A plaintiff
is under no obligation to ‘produce’ its evidence prior to trial,
unless such an obligation arose in response to a discovery
demand (or a court order) requiring the plaintiff to set forth
MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.               17



the evidence supporting its claim.” Nick’s Garage, 875 F.3d
at 115. As far as we have been shown, Facebook has not
made a discovery demand that Mirror Worlds identify all
its evidence for the “every data unit” limitation. Given that
discovery is still open, Mirror Worlds may still muster evi-
dence to prove its claim. Facebook has not otherwise
shown that sufficient evidence cannot be produced.
    When Facebook moved for summary judgment, having
been allowed to file such a motion even before discovery
closed, its attempt to “show” entitlement to summary judg-
ment rested on one assertion: that TAO does not store in-
formation in a time-ordered sequence. J.A. 1095–97;
J.A. 1092–94. Facebook did not assert that the record
lacked evidence of infringement even if TAO is not part of
the “computer system.” Mirror Worlds, in arguing that the
accused “computer system[s]” do not include TAO, met the
ground asserted by Facebook, and the district court did not
conclude otherwise. Mirror Worlds, in fact, went further.
As recounted above, it identified the accused “systems,” it
described (with evidentiary support) how those systems
work, and it asserted based on that description that Leaves
and TimelineDB meet the “every data unit” requirement
and hence are “main streams.” Although the district court
concluded that Mirror Worlds’ response failed in one par-
ticular respect, that conclusion is erroneous, as already dis-
cussed. On this record, we are not required, and we do not
think it appropriate, to declare on appeal that Mirror
Worlds’ opposition was categorically insufficient to with-
stand summary judgment.
    Second, Facebook points to certain information that it
argues is received by the two back-end systems that is not
included in Leaves or TimelineDB: information from Ad-
finder and Ego for Multifeed; certain query criteria for the
Timeline back-end system. But although Facebook men-
tioned these points at the oral argument before the district
court, see J.A. 119–20, it did not present them in its motion
or even its reply in the district court, leaving Mirror Worlds
18           MIRROR WORLDS TECHNOLOGIES v. FACEBOOK, INC.




without a fair opportunity to address them. And the dis-
trict court did not address these points, which raise ques-
tions about, among other things, whether this information
comes within the relevant claim terms, e.g., “data units,”
under a proper construction.
    In these circumstances, we will not adopt Facebook’s
alternative arguments for affirmance. Our ruling is with-
out prejudice to otherwise-appropriate consideration of
non-infringement contentions on remand, especially once
the record is fully developed.
                             C
    To the extent that the district court’s construction of
“main collection” and “subcollection” apply beyond Face-
book’s summary-judgment motion, Mirror Worlds asks us
to vacate those constructions. We do not read the court’s
opinion as having construed the terms with any such effect.
The district court stated that, despite the parties’ dispute,
the terms “main collection” and “subcollection” “present
identical issues for purposes of this motion” as the terms
“main stream” and “substream,” respectively. Mirror
Worlds, 320 F. Supp. 3d at 543–44. We understand that
statement to go no further than indicating that any differ-
ence between those terms does not matter given the ground
on which the court decided the case. We have reversed that
ground for summary judgment. The claim-construction is-
sue is open on remand.
                             III
    For the foregoing reasons, we reverse the district
court’s summary judgment of non-infringement. We re-
mand the case for further proceedings.
     Costs awarded to Mirror Worlds.
            REVERSED AND REMANDED
