628
Opinion of the Court
that basis for finding appellate jurisdiction. Second, if respondent's constitutional claim, discussed in Part III, infra, were sound, her sentence would have been "imposed in violation of law." Thus, if she had prevailed on the merits, her victory would also have confirmed the jurisdiction of the Court of Appeals.
Although we ultimately conclude that respondent's sentence was not "imposed in violation of law" and therefore that § 3742(a)(1) does not authorize an appeal in a case of this kind, it is familiar law that a federal court always has jurisdiction to determine its own jurisdiction. See United States v. Mine Workers, 330 U. S. 258, 291 (1947). In order to make that determination, it was necessary for the Ninth Circuit to address the merits. We therefore hold that appellate jurisdiction was proper.
III
The constitutional question concerns a federal criminal defendant's waiver of the right to receive from prosecutors exculpatory impeachment material—a right that the Constitution provides as part of its basic "fair trial" guarantee. See U. S. Const., Amdts. 5, 6. See also Brady v. Maryland, 373 U. S. 83, 87 (1963) (Due process requires prosecutors to "avoi[d] . . . an unfair trial" by making available "upon request" evidence "favorable to an accused . . . where the evidence is material either to guilt or to punishment"); United States v. Agurs, 427 U. S. 97, 112-113 (1976) (defense request unnecessary); Kyles v. Whitley, 514 U. S. 419, 435 (1995) (exculpatory evidence is evidence the suppression of which would "undermine confidence in the verdict"); Giglio v. United States, 405 U. S. 150, 154 (1972) (exculpatory evidence includes "evidence affecting" witness "credibility," where the witness' "reliability" is likely "determinative of guilt or innocence").
When a defendant pleads guilty he or she, of course, for-goes not only a fair trial, but also other accompanying consti-
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