In the

United States Court of Appeals

For the Seventh Circuit

Nos. 99-2770 and 99-2843

Ferdinand Pickett,

Plaintiff-Appellant, Cross-Appellee,

v.

Prince,

Defendant-Appellee, Cross-Appellant.

Appeals from the United States District Court

for the Northern District of Illinois, Eastern Division.

No. 94 C 4740--

Rebecca R. Pallmeyer & Milton I. Shadur, Judges.

Argued February 18, 2000--Decided March 14, 2000

 Before Posner, Chief Judge, and Bauer and Manion,

Circuit Judges.

 Posner, Chief Judge. The appeal by Ferdinand

Pickett, plaintiff in the district court,

presents us with an issue concerning copyright in

derivative works, while the cross-appeal, by the

defendant, presents a procedural issue. The

defendant, identified only as "Prince" in the

caption of the various pleadings, is a well-known

popular singer whose name at birth was Prince

Rogers Nelson, but who for many years performed

under the name Prince (which is what we’ll call

him) and since 1992 has referred to himself by an

unpronounceable symbol reproduced as Figure 1 at

the end of this opinion. (See generally "The

Independent, Unofficial and Uncensored Magazine

Exploring the Artist Formerly Known as Prince,"

<http://www.uptown.se/>.) The symbol (which

rather strikingly resembles the Egyptian

hieroglyph ankh, see Richard H. Wilkinson, Symbol

& Magic in Egyptian Art 159, 169 (fig. 128)

(1994), but the parties make nothing of this, so

neither shall we) is his trademark but it is also

a copyrighted work of visual art that licensees

of Prince have embodied in various forms,

including jewelry, clothing, and musical

instruments. Although Prince did not register a

copyright of the symbol until 1997, the plaintiff
concedes that Prince obtained a valid copyright

in 1992, registration not being a precondition to

copyright protection, 17 U.S.C. sec. 408(a),

though it’s a precondition to a suit for

copyright infringement. sec. 411(a); Raquel v.

Education Mgmt. Corp., 196 F.3d 171, 176 (3d Cir.

1999). Actually the original copyright was not

obtained by him, but he is the assignee, and the

assignment expressly granted him the right to sue

for infringement of the copyright before the

assignment.

 In 1993 the plaintiff made a guitar (Figure 2)

in the shape of the Prince symbol; he concedes

that it is a derivative work within the meaning

of 17 U.S.C. sec. 101 ("a work based upon one or

more preexisting works, such as a translation,

musical arrangement, dramatization,

fictionalization, motion picture version, sound

recording, art reproduction, abridgment,

condensation, or any other form in which a work

may be recast, transformed, or adapted. A work

consisting of editorial revisions, annotations,

elaborations, or other modifications which, as a

whole, represent an original work of authorship,

is a ’derivative work’"). The plaintiff claims

(truthfully, we assume for purposes of the

appeal) to have shown the guitar to Prince.

Shortly afterwards Prince appeared in public

playing a guitar quite similar to the plaintiff’s

(Figure 3).

 The plaintiff brought this suit for copyright

infringement in 1994, but it languished for years

in the district court. In January 1997 Prince

counterclaimed for infringement of the copyright

on his symbol, arguing (because he had not yet

registered his copyright--indeed it hadn’t even

been assigned to him yet) that in 1992 Warner

Brothers had registered a copyright of the symbol

in connection with a record of Prince’s music.

Prince was mistaken; the copyright was of the

music, not of the symbol, although the symbol

appeared on the album cover. In any event Prince

had no standing to enforce someone else’s

copyright--so that, if only Warner Brothers held

a copyright on the Prince symbol, Prince would

have no defense against Pickett’s suit for

infringement (or at least would not have the

defense that he successfully asserted in the

district court), as well as no basis for a

counterclaim. In July 1997, however, on the

Monday following the third anniversary of

Pickett’s suit (which fell on a Saturday), Prince

filed an amended counterclaim for infringement,

claiming that it was his own, not Warner

Brothers’, copyright that Pickett’s guitar

infringed; for between January and July Prince

had obtained the copyright by assignment and had

registered it. The district court (Judge Shadur)
held that the amended counterclaim, which

superseded the original one, did not relate back

to the original counterclaim because it did not

arise out of the same copyright, and so it was

barred by the three-year statute of limitations

for claims of copyright infringement. 17 U.S.C.

sec. 507(b). Later the suit was transferred to

Judge Pallmeyer, who on Prince’s motion for

summary judgment dismissed Pickett’s claim on the

ground that he had no right to make a derivative

work based on the Prince symbol without Prince’s

consent, which was never sought or granted. 52 F.

Supp. 2d 893 (N.D. Ill. 1999).

 Pickett claims the right to copyright a work

derivative from another person’s copyright

without that person’s permission and then to sue

that person for infringement by the person’s own

derivative work. Pickett’s guitar was a

derivative work of the copyrighted Prince symbol,

and so was Prince’s guitar. Since Prince had (or

so we must assume) access to Pickett’s guitar,

and since the two guitars, being derivatives of

the same underlying work, are, naturally, very

similar in appearance, Pickett has-- if he is

correct that one can copyright a derivative work

when the original work is copyrighted by someone

else who hasn’t authorized the maker of the

derivative work to copyright it--a prima facie

case of infringement. Wildlife Express Corp. v.

Carol Wright Sales, Inc., 18 F.3d 502, 508 (7th

Cir. 1994); Procter & Gamble Co. v. ColgatePalmolive Co., 199 F.3d 74, 77 (2d Cir. 1999)

(per curiam); Castle Rock Entertainment, Inc. v.

Carol Publishing Group, Inc., 150 F.3d 132, 137

(2d Cir. 1998); Twin Peaks Productions, Inc. v.

Publications International, Ltd., 996 F.2d 1366,

1372 (2d Cir. 1993); see also 2 Paul Goldstein,

Copyright: Principles, Law and Practice sec.

7.2.1, p. 8 (1989) ("the fact that the defendant

had access to the plaintiff’s work and that the

defendant’s work is similar to the plaintiff’s

can form the basis for an inference that the

defendant copied her work from the plaintiff’s

work"). Pickett must, he concedes, show that his

derivative work has enough originality to entitle

him to a copyright, and also that the copyright

is limited to the features that the derivative

work adds to the original. But he insists that

with these limitations his copyright is valid.

 We doubt that he could show the requisite

incremental originality, Lee v. A.R.T. Co., 125

F.3d 580 (7th Cir. 1997); Gracen v. Bradford

Exchange, 698 F.2d 300, 304-05 (7th Cir. 1983),

slight as it need be. Feist Publications, Inc. v.

Rural Telephone Service Co., 499 U.S. 340, 345,

362-63 (1991); CDN Inc. v. Kapes, 197 F.3d 1256,

1259-61 (9th Cir. 1999); Acuff-Rose Music, Inc.

v. Jostens, Inc., 155 F.3d 140, 143-44 (2d Cir.
1998); 1 Melville B. Nimmer & David Nimmer,

Nimmer on Copyright sec. 3.03, p. 3-10 (1999);

see generally 1 Goldstein, supra, sec. 2.2.1, pp.

62-65. In Lee v. A.R.T. Co., supra, 125 F.3d at

582, we noted a conflict in the authorities over

whether any originality is required for a

derivative work. We had explained in Gracen v.

Bradford Exchange, supra, 698 F.2d at 304, and

we’ll note later in this opinion as well, that

such a requirement is essential in order to head

off situations in which it is impossible to

adjudicate a dispute between owners of two

derivative works because the works are identical

both to the original and to each other. The Ninth

Circuit, the only court cited in Lee as

disagreeing with us, had, in fact, swung around

to our view shortly before our decision came

down. Entertainment Research Group, Inc. v.

Genesis Creative Group, Inc., 122 F.3d 1211, 1220

(9th Cir. 1997).

 Although Pickett’s guitar isn’t identical to the

Prince symbol, the difference in appearance may

well be due to nothing more than the functional

difference between a two-dimensional symbol and a

guitar in the shape of that symbol. In that event

even Prince could not have copyrighted the guitar

version of the symbol. 17 U.S.C. sec. 101;

American Dental Ass’n v. Delta Dental Plans

Ass’n, 126 F.3d 977, 980 (7th Cir. 1997);

Entertainment Research Group, Inc. v. Genesis

Creative Group, Inc., supra, 122 F.3d at 1221-24;

cf. Mitel, Inc. v. Iqtel, Inc., 124 F.3d 1366,

1374-75 (10th Cir. 1997); Williams v. Crichton,

84 F.3d 581, 587-88 (2d Cir. 1996). A guitar

won’t work without strings, frets, etc. arranged

in a pattern dictated by musical considerations,

and to the extent that the pattern is what it is

because otherwise the guitar won’t sound right,

it is not copyrightable as a work of visual art.

Maybe, though, the juxtaposition of the symbol

and the guitar is enough to confer on the

ensemble sufficient originality as a work of

visual art to entitle the designer to copyright

it. See North Coast Industries v. Jason Maxwell,

Inc., 972 F.2d 1031 (9th Cir. 1992); Rogers v.

Koons, 960 F.2d 301, 307 (2d Cir. 1992). Many

works of art rely for their effect on the

juxtaposition of familiar elements ordinarily

held separate (like a mustache painted on a

photograph of the Mona Lisa); indeed, all works

of art are ultimately combinations of familiar,

uncopyrightable items.

 We need not pursue the issue of originality of

derivative works. The Copyright Act grants the

owner of a copyright the exclusive right to

prepare derivative works based upon the

copyrighted work. 17 U.S.C. sec. 106(2); Lee v.

A.R.T. Co., supra, 125 F.3d at 581; Gracen v.
Bradford Exchange, supra, 698 F.2d at 302; Atari,

Inc. v. North American Philips Consumer

Electronics Corp., 672 F.2d 607, 618 n. 12 (7th

Cir. 1982); Micro Star v. Formgen Inc., 154 F.3d

1107, 1110 (9th Cir. 1998). So Pickett could not

make a derivative work based on the Prince symbol

without Prince’s authorization even if Pickett’s

guitar had a smidgeon of originality. This is a

sensible result. A derivative work is, by

definition, bound to be very similar to the

original. Concentrating the right to make

derivative works in the owner of the original

work prevents what might otherwise be an endless

series of infringement suits posing insoluble

difficulties of proof. Consider two translations

into English of a book originally published in

French. The two translations are bound to be very

similar and it will be difficult to establish

whether they are very similar because one is a

copy of the other or because both are copies of

the same foreign-language original. Whether

Prince’s guitar is a copy of his copyrighted

symbol or a copy of Pickett’s guitar is likewise

not a question that the methods of litigation can

readily answer with confidence. If anyone can

make derivative works based on the Prince symbol,

we could have hundreds of Picketts, each charging

infringement by the others.

 Pickett relies for his implausible theory

primarily on section 103(a) of the Copyright Act,

which provides that while copyright can be

obtained in derivative works, "protection for a

work employing preexisting material in which

copyright subsists does not extend to any part of

the work in which such material has been used

unlawfully." Pickett reads this as authorizing a

person other than the owner of the original work

to make a derivative work, merely forbidding him

to infringe the original. It is very difficult to

see how a derivative work not made by the owner

of the original work could fail to infringe it,

given the definition of derivative works. (There

is no infringement by the owner of the copyright

of the original work, since section 106(2)

entitles him to make derivative works based on

his copyrighted work. Cortner v. Israel, 732 F.2d

267, 271 (2d Cir. 1984).) Picket doesn’t deny

this; having warded off (he thinks) Prince’s

counterclaim for copyright infringement, he is

unafraid to acknowledge that he is an infringer

and to content himself with arguing that his

copyright extends only to the original elements

of the infringing work. But we do not read

section 103(a) as qualifying the exclusive right

of the owner of the copyright of the original

work to make derivative works based on that work,

the right conferred by section 106(2). Section

103(a) means only, at least so far as bears on

this case, that the right to make a derivative
work does not authorize the maker to incorporate

into it material that infringes someone else’s

copyright. Cortner v. Israel, supra, 732 F.2d at

272; 1 Nimmer & Nimmer, supra, sec. 3.06, pp. 3-

34.23 to 3-34.27; cf. Harris Custom Builders,

Inc. v. Hoffmeyer, 92 F.3d 517, 519 (7th Cir.

1996). So if Pickett owned a copyright of, say, a

picture of Prince, and Prince used that picture

in his own guitar without Pickett’s consent,

Pickett would have a claim of infringement. But

the only copyright that Pickett claims Prince

infringed is a copyright that Pickett had no

right to obtain, namely a copyright on a

derivative work based on Prince’s copyrighted

symbol.

 Pickett relied in the district court on a dictum

in Eden Toys, Inc. v. Florelee Undergarment Co.,

697 F.2d 27, 34 n. 6 (2d Cir. 1982), that a

stranger can make a derivative work without the

permission of the owner of the copyright of the

original work if the original work does not

"pervade" the derivative work. The suggestion, if

taken seriously (which it has not been), would

inject enormous uncertainty into the law of

copyright and undermine the exclusive right that

section 106(2) gives the owner of the copyright

on the original work. It also rests on a

confusion between the determination of whether a

work is derivative and the determination of who

has the right to make the derivative work.

Defined too broadly, "derivative work" would

confer enormous power on the owners of copyrights

on preexisting works. The Bernstein-Sondheim

musical West Side Story, for example, is based

loosely on Shakespeare’s Romeo and Juliet, which

in turn is based loosely on Ovid’s Pyramus and

Thisbe, so that if "derivative work" were defined

broadly enough (and copyright were perpetual)

West Side Story would infringe Pyramus and Thisbe

unless authorized by Ovid’s heirs. We can thus

imagine the notion of pervasiveness being used to

distinguish a work fairly described as derivative

from works only loosely connected with some

ancestral work claimed to be their original. Cf.

Micro Star v. Formgen Inc., supra, 154 F.3d at

1110. In that sense Prince’s symbol clearly

"pervades" both guitars. If it did not, the

guitars might not be derivative works, but they

would not be derivative works that anyone was

free to make without obtaining Prince’s

permission.

 It is apparent from what we have said so far not

only that Pickett could not copyright his guitar,

but that his guitar infringes Prince’s copyright.

(Pickett’s further argument, that Prince’s

copyright has evaporated if, as Judge Shadur

ruled, the counterclaim to enforce it is timebarred and so Prince’s symbol fell into the
public domain and became fair game for makers of

derivative works, is ridiculous.) The remaining

question, whether the counterclaim was properly

dismissed on the basis of the statute of

limitations, is the subject of Prince’s crossappeal. Oddly, there is not the slightest doubt

that the amended counterclaim was filed before

the statute of limitations expired, and this

regardless of whether it related back to the

original, Fed. R. Civ. P. 15(c)(2), as probably

it did not, since it was based on a different

copyright. Cf. 6A Charles Alan Wright, Arthur R.

Miller & Mary Kay Kane, Federal Practice and

Procedure sec. 1497, pp. 70-74 (1990). Although

the amended counterclaim was filed on the last

possible day before expiration, namely the Monday

after the Saturday that was the third anniversary

of the filing of Pickett’s suit, see Fed. R. Civ.

P. 6(a), the adage that a miss is as good as a

mile applies in reverse here: a suit is timely

whether filed the day after the claim accrues or

the very last day before the suit would be timebarred.

 So why was the counterclaim dismissed as

untimely? The three-year period of limitations

began running on July 5, 1994, and the judge

ruled that the counterclaim was untimely because

it had not been filed until July 7, 1997.

Apparently no one, including the judge, noticed

that July 5, 1997, was a Saturday. Prince’s

lawyer finally woke up, and a couple of weeks

after Judge Shadur had ruled filed a motion for

reconsideration which the judge denied on the

ground that a motion for reconsideration is not

an appropriate vehicle for injecting a new legal

theory into a case.

 We think that in so ruling the judge abused his

discretion. Unlike the case in which a judgment

is sought to be vacated, to which the principle

enunciated by the judge does apply, e.g., Caisse

Nationale de Credit Agricole v. CBI Industries,

Inc., 90 F.3d 1264, 1269-70 (7th Cir. 1996);

Keene Corp. v. International Fidelity Ins. Co.,

736 F.2d 388, 393 (7th Cir. 1984), although its

application to a computational error having

nothing to do with legal "theory" may be doubted,

see Russell v. Delco Remy Division, 51 F.3d 746,

749 (7th Cir. 1995), a motion to reconsider a

ruling is constrained only by the doctrine of the

law of the case. And that doctrine is highly

flexible, especially when a judge is being asked

to reconsider his own ruling. Avitia v.

Metropolitan Club of Chicago, Inc., 49 F.3d 1219,

1227 (7th Cir. 1995); Prisco v. A & D Carting

Corp., 168 F.3d 593, 607 (2d Cir. 1999). Judge

Shadur’s ruling that the counterclaim was

untimely was interlocutory, and thus not a final

judgment. In fact, it was not a judgment at all.
It was issued in December of 1997, and the final

decision by the district court didn’t come until

June 18 of last year. The ruling was also the

plainest of plain errors, requiring only a glance

at the calendar to discover. The judge was led

into the plain error by the party seeking to

correct it, but that is often the case. Had

Prince’s lawyer discovered the error a few weeks

earlier and brought it to Judge Shadur’s

attention before the judge ruled, undoubtedly the

judge would have held that the counterclaim was

timely.

 Although we can understand Judge Shadur’s

annoyance at being led into plain error, a

judge’s refusal to correct a plain error that he

had committed weeks before is not justified by

the doctrine of the law of the case, or anything

else we can think of. Creek v. Village of

Westhaven, 144 F.3d 441, 446 (7th Cir. 1998);

Evans v. City of Chicago, 873 F.2d 1007, 1013-14

(7th Cir. 1989); United States v. Zanghi, 189

F.3d 71, 79-80 (1st Cir. 1999). Were we to uphold

the denial of reconsideration and dismissal of

the counterclaim, we would be penalizing Prince’s

lawyer for having asked Judge Shadur to correct

his own mistake, rather than reserving the issue

for an appeal, and we would thus be discouraging

efforts by litigants to purge errors before the

case comes to us (perhaps it won’t come to us if

the errors are purged). For if Prince had for the

first time on appeal argued that Judge Shadur had

erred in dismissing the counterclaim as untimely,

and if Pickett had responded that Prince had

waived the issue by failing to raise it in the

district court, Prince would have appealed to the

doctrine of plain error to absolve him from the

consequences of the waiver. And limited though

that doctrine is in civil cases, see, e.g., Deppe

v. Tripp, 863 F.2d 1356, 1360-61 (7th Cir. 1988);

Smith v. Kmart Corp., 177 F.3d 19, 28 (1st Cir.

1999), we would have invoked it and reversed the

dismissal of the counterclaim. The result should

not be different merely because, though apprised

of the error, Judge Shadur refused to correct it.

 It is conceivable though not argued that

Prince’s failure to discover that July 5, 1997,

was a Saturday (or to realize the significance of

the fact) was harmful to Pickett; but such an

argument would get nowhere, for it was as

irresponsible for Pickett’s lawyer to argue the

untimeliness of a counterclaim that he should

have known was timely as it was for Prince’s

lawyer to fail to refute the argument. As no

effort was made to show that Pickett was harmed

by Prince’s mistake (and it was, to repeat,

Pickett’s mistake as well), let alone so gravely

harmed as to warrant the dismissal of the

counterclaim rather than just an order that
Prince reimburse Pickett for any expense

occasioned by the mistake, we cannot think of any

reason at all why Judge Shadur should have

refused to rescind his erroneous dismissal of the

counterclaim.

 The judgment is affirmed insofar as it dismisses

Pickett’s suit but vacated insofar as it

dismisses the counterclaim, and the case is

remanded for further proceedings consistent with

this opinion.

Affirmed in Part,

Vacated in Part,

and Remanded.

Figure 1

Figure 2

Figure 3