207 F.3d 402 (7th Cir. 2000)
Ferdinand Pickett,    Plaintiff-Appellant, Cross-Appellee,v.Prince,    Defendant-Appellee, Cross-Appellant.
Nos. 99-2770 and 99-2843
In the  United States Court of Appeals  For the Seventh Circuit
Argued February 18, 2000Decided March 14, 2000

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.
Before Posner, Chief Judge, and Bauer and Manion,  Circuit Judges.
Posner, Chief Judge.


1
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.


2
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).


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).


4
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. Colgate-  Palmolive 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.


5
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).


6
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.


7
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.


8
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.


9
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.


10
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 time-  barred 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 cross-  appeal. 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 time-  barred.


11
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.


12
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.


13
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.


14
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.


15
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.


16
Affirmed in Part,  Vacated in Part,  and Remanded. [Tabular or Graphical Material Omitted]


17
FIG. 1                                  FIG. 3


18
[Tabular or Graphical Material Omitted]


19
Figure 1[Tabular or Graphical Material Omitted]

Figure 2
