In the

United States Court of Appeals

For the Seventh Circuit

No. 00-2257

Fredric Karl Saecker,

Plaintiff-Appellant,

v.

William H. Thorie and Doar, Drill & Skow, S.C.,

Defendants-Appellees.

Appeal from the United States District Court

for the Western District of Wisconsin.

No. 99-C-671-S--John C. Shabaz, Chief Judge.

Argued November 15, 2000--Decided December 12, 2000

 Before Posner, Easterbrook, and Kanne, Circuit Judges.

 Posner, Circuit Judge. This is a diversity suit

for legal malpractice, and at once we confront an

issue of federal subject-matter jurisdiction. The

plaintiff’s jurisdictional statement, in

violation of 7th Cir. R. 28(a)(1), does not

indicate the state of citizenship of either the

plaintiff or the defendants, who compound the

error in their jurisdictional statement by

failing both to point out the error and to supply

the missing information. From the record it is

apparent that the plaintiff is a citizen of

Minnesota and the individual defendant a citizen

of Wisconsin; but what of the law-firm defendant?

The name of the firm is followed by "S.C.," and

while its counsel informs us that this means

"service corporation" and that the firm is

incorporated and has its principal place of

business in Wisconsin, he confessed to being

unacquainted with the nature of a Wisconsin

service corporation either generally or in

reference to its status for purposes of the

diversity jurisdiction. If the service

corporation is assimilated to a regular business

corporation, then jurisdiction is of course

secure; but if it is assimilated to a

partnership, including a limited partnership, or

to an L.L.C. (limited-liability company), the

existence of diversity would depend on the

citizenship of the partners, Carden v. Arkoma

Associates, 494 U.S. 185, 195-96 (1990); Northern
Trust Co. v. Bunge Corp., 899 F.2d 591, 594 (7th

Cir. 1990); Cosgrove v. Bartolotta, 150 F.3d 729,

731 (7th Cir. 1998), which the record does not

disclose.

 The answer is given by our decision in Cote v.

Wadel, 796 F.2d 981, 983 (7th Cir. 1986), where

we held, primarily to avoid multiplying confusing

distinctions within the category of corporations,

that a professional corporation is to be treated

the same as a regular business corporation, even

if the professional corporation does not protect

its principals from personal liability or serve

to raise capital from passive investors. See also

Saxe, Bacon & Bolan, P.C. v. Martindale, Hubbell,

Inc., 710 F.2d 87, 89 (2d Cir. 1983); cf. CCC

Information Services, Inc. v. American Salvage

Pool Ass’n, 230 F.3d 342, 346 (7th Cir. 2000);

National Ass’n of Realtors v. National Real

Estate Ass’n, Inc., 894 F.2d 937, 939 (7th Cir.

1990); Mutual Service Casualty Ins. Co. v.

Country Life Ins. Co., 859 F.2d 548, 550-51 (7th

Cir. 1988). "Service corporation" is Wisconsin’s

name for professional corporation, see Wis. Stat.

sec.sec. 180.901-.921; Wausau Medical Center,

S.C. v. Asplund, 514 N.W.2d 34, 37, 44 (Wis. App.

1994), and so comes within the rule of the Cote

case.

 Cote was a "first generation" professionalcorporation case. The original impetus for the

formation of professional corporations was to

obtain tax benefits, not to limit liability. Even

today, some professional-corporation statutes do

not limit the personal liability of the

principals of such a corporation, corresponding

to partners in the traditional law-firm

partnership. But many do. (See the useful

discussions in Christopher C. Wang, "Breaking Up

Is Hard to Do: Allocation of Fees From the

Unfinished Business of a Professional

Corporation," 64 U. Chi. L. Rev. 1367 (1997), and

Debra L. Thill, "The Inherent Powers Doctrine and

Regulation of the Practice of Law: Will Minnesota

Attorneys Practicing in Professional Corporations

or Limited Liability Companies Be Denied the

Benefit of Statutory Liability Shields?" 20 Wm.

Mitchell L. Rev. 1143 (1994).) Wisconsin’s

service-corporation statute is one of them. It

protects the shareholders of such a corporation

from vicarious liability for the negligence or

other misconduct either of the corporation itself

or of the other shareholders. Wis. Stat. sec.

180.1915. The statute does not shield the lawyer

or other professional from unlimited liability

for acts of the corporation in which he is

personally complicit; and that means that if a

lawyer practicing by himself incorporates as a

service corporation, he obtains no limitation of

his personal liability at all. But that is
equally true of the limited liability of

shareholders of ordinary business corporations:

they are not insulated from unlimited personal

liability for acts on behalf of the corporation

for which they could be sued personally.

 There is thus no tension with National Ass’n of

Realtors v. National Real Estate Ass’n, Inc.,

supra, 894 F.2d at 940, which carved an exception

to the rule of Cote v. Wadel for cases in which

the shareholders of a corporation rather than the

corporation itself are the real parties in

interest; in that case it is their citizenship,

not that of the corporation, that counts. See

also CCC Information Services, Inc. v. American

Salvage Pool Ass’n, supra, 230 F.3d at 347;

Northern Trust Co. v. Bunge Corp., supra, 899

F.2d at 594. The exception is inapplicable to

this case. Apart from Thorie himself, the

personal assets of the shareholders of Doar,

Drill & Skrow, S.C., are not at risk.

 Any tension between Cote and later cases derives

not from National Ass’n of Realtors v. National

Real Estate Ass’n but from the limited

partnership and L.L.C. cases, since,

functionally, they are even closer to standard

business corporations than are professional (or

service) corporations yet they are treated as

ordinary partnerships for purposes of determining

whether there is diversity jurisdiction. But as

neither party has asked us to reexamine Cote, and

no case has questioned its rule, and the

Wisconsin service-corporation goes far to

assimilate professional to standard business

corporations, we shall adhere to the rule of that

case at least for now.

 On the merits, the district judge granted

summary judgment for the defendants on the ground

that Wisconsin’s six-year statute of limitations

for legal malpractice, Wis. Stat. sec. 893.53,

had run. In January of 1990, the plaintiff,

Saecker, represented by the individual defendant,

Thorie (a member of the defendant firm), had been

convicted in a Wisconsin state court of rape and

other crimes and sentenced to 15 years in prison.

Saecker’s family had wanted DNA testing of bodily

fluids and hair found on the victim of the rape,

but Thorie had advised against this on the

erroneous ground that the results of DNA testing

would not be admissible at Saecker’s trial.

Saecker’s appellate remedies were exhausted on

April 2, 1991, but in subsequent postconviction

proceedings in which he was represented by new

counsel he successfully moved for the DNA

testing, which exonerated him. In October of

1996, after a new trial was ordered, all charges

against him were dropped. He brought this suit in

May of 1999. The district court ruled that the
statute of limitations had begun to run on April

2, 1991, when the Wisconsin Supreme Court denied

Saecker’s petition to review the affirmance of

his conviction, and so expired before he brought

his suit.

 Under Wisconsin law a statute of limitations

begins to run when the plaintiff discovers or

should have discovered both his injury and the

person who, and the act that, were the probable

cause of the injury. See Borello v. U.S. Oil Co.,

388 N.W.2d 140, 146 (Wis. 1986); Smith v.

Herrling, Myse, Swain & Dyer, Ltd., 565 N.W.2d

809, 811 (Wis. App. 1997); Wiskunas v. Birnbaum,

23 F.3d 1264, 1266 (7th Cir. 1994). He needn’t

know that he has a claim against that person for

that act; he has the statutory period to

determine whether he has a claim and if so to

prepare and file his suit, and that is time

enough given that he knows that he has been

injured and knows also who injured him and by

what conduct.

 The parties agree that the date of injury was

April 2, 1991, and in view of their agreement we

need not speculate on alternative possibilities,

such as the date of his conviction. Cf. Smith v.

Herrling, Myse, Swain & Dyer, Ltd., supra, 565

N.W.2d at 811-12. The quarrel is over the date on

which Saecker discovered or should have

discovered that the likely cause of the injury

was Thorie’s failure to obtain a DNA test that

would have averted the conviction. April 2, 1991,

the date selected by the district court, is too

early. Saecker had no reason to believe that

Thorie was giving him erroneous advice about the

admissibility of DNA evidence. He had no reason

to believe, therefore, that his conviction had

been caused by a decision of his lawyer. He did

have reason to believe this by January 17, 1993,

the date on which his new lawyer moved for an

order to conduct a DNA test; and this date was

more than six years before he sued. He could not

be certain then that Thorie had injured him by

failing to have made such a motion, because he

could not be certain what the outcome of the test

would be. The fact that he passed the test,

however, suggests that he had a good idea he

would pass it (that is, he knew he was innocent).

He knew enough, we think, to have set the statute

of limitations running. See id. at 811; Wiskunas

v. Birnbaum, supra, 23 F.3d at 1266.

 Though not mentioned by the parties, the

Wisconsin courts might hold that the statute of

limitations was tolled until October 1996, when

the state finally dropped all charges against

Saecker. In most states, including Wisconsin, a

legal malpractice suit against a criminal defense

attorney requires a showing that the criminal
defendant (that is, the malpractice plaintiff)

actually was innocent, implying acquittal and

more--that the defendant really was innocent and

wasn’t just acquitted because the state could not

carry its heavy burden of proof. E.g., Harris v.

Bowe, 505 N.W.2d 159, 162 (Wis. App. 1993);

Mahoney v. Shaheen, Cappiello, Stein & Gordon,

727 A.2d 996, 998-99 (N.H. 1999); Wiley v. County

of San Diego, 966 P.2d 983, 991 (Cal. 1998);

Peeler v. Hughes & Luce, 909 S.W.2d 494, 497-98

(Tex. 1995). The thinking behind this rule is

that a guilty person should not be allowed to

reduce his punishment by getting a money judgment

against his lawyer.

 Until October 1996, Saecker’s innocence had not

been determined. But if therefore the running of

the statute of limitations was tolled until then,

this would not help him. The doctrine of

equitable tolling, the doctrine that is

applicable when a plaintiff seeks tolling for

reasons other than acts by the defendant that

prevented him from suing earlier, requires the

plaintiff to sue as early as he can after

expiration of the statute of limitations. E.g.,

Elmore v. Henderson, 227 F.3d 1009, 1013 (7th

Cir. 2000); United States v. Duke, 229 F.3d 627,

630-31 (7th Cir. 2000). Saecker had no excuse for

waiting two and a half years after the charges

against him were dropped to bring his malpractice

suit.

 The suit is also barred by the doctrine of

judicial estoppel, which forbids a party who has

prevailed in one suit to repudiate the ground on

which he prevailed in order to win a subsequent

suit. E.g., United States v. Hook, 195 F.3d 299,

306 (7th Cir. 1999); Ogden Martin System of

Indianapolis, Inc. v. Whiting Corp., 179 F.3d

523, 526-27 (7th Cir. 1999). Previous federal

cases have treated it as a federal procedural

doctrine applicable regardless of the version of

the doctrine embraced by the state that rendered

the judgment sought to be used to work the

estoppel. Ogden Martin Systems of Indianapolis,

Inc. v. Whiting Corp., supra, 179 F.3d at 527 n.

1; Edwards v. Aetna Life Ins. Co., 690 F.2d 595,

597 n. 4 (6th Cir. 1982); Allen v. Zurich Ins.

Co., 667 F.2d 1162, 1167 n. 4 (4th Cir. 1982).

They have reasoned as follows: the purpose of the

doctrine is to reduce the temptation to fraud in

litigation, Ladd v. ITT Corp., 148 F.3d 753, 756

(7th Cir. 1998); State v. Perry, 548 N.W.2d 817,

821 (Wis. 1996); the interest of the second court

(the one the winner of a previous suit wishes to

persuade on the basis of a ground that he

successfully fought against in that suit) in not

being defrauded is as great as the interest of

the first court; the doctrine is therefore part

of the second court’s arsenal of self-protective
weaponry.

 This conclusion is in tension, however, with 28

U.S.C. sec. 1738, as interpreted by the Supreme

Court in Marrese v. American Academy of

Orthopaedic Surgeons, 470 U.S. 373 (1985). In

holding that section 1738 requires federal courts

to apply the preclusion (res judicata and

collateral estoppel) principles of the state

whose judgment is sought to be used to block

relitigation, the Court expressly rejected, id.

at 385, the argument (which this court, in the

decision that the Court reversed, had adopted,

726 F.2d 1150, 1154 (7th Cir. 1984) (en banc)

(plurality opinion)) that since preclusion is

intended to conserve judicial resources as well

as to spare parties the expense and uncertainty

of relitigation, the court asked to give

preclusive weight to an earlier judgment should

be entitled to give weight to its own views of

the proper scope of preclusion. Judicial estoppel

is a kind of preclusion doctrine, and here it is

a judgment of the State of Wisconsin that is

sought to be used to preclude relitigation of an

issue (the issue of Thorie’s negligence).

 We need not try to resolve the tension in that

case. Wisconsin has a doctrine of judicial

estoppel, and it is identical to the federal

doctrine. See State v. Perry, supra, 548 N.W.2d

at 821-22, referring approvingly to federal

cases, including cases of this court. As there is

no conflict between the federal and Wisconsin

versions of the doctrine, we can proceed to apply

it without resolving the issue flagged in the

preceding paragraph.

 When Saecker, having in postconviction

proceedings obtained the DNA test results, moved

for a new trial on the basis of newly discovered

evidence, he had to show that the evidence had

not been available to him at trial. Part of the

explanation that he offered, embracing Thorie’s

unsound advice, was that DNA evidence was

believed to be inadmissible--which if true would

eliminate the basis for his malpractice claim.

The Wisconsin courts that adjudicated his motion

for a new trial duly held that DNA testing had

been such a novelty in 1990 that Saecker, and so

by implication Thorie, could not be faulted for

not having moved for such testing. This ruling is

inconsistent with the malpractice claim, which

Saecker could have preserved only by arguing in

the postconviction proceedings that his failure

to move for DNA testing at trial was due not to

DNA evidence being inadmissible but rather to

ineffective assistance by his trial counsel.

Affirmed.