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Rh Rh Seldin, 422 U.S. 490, 498 (1975). The latter are "essentially matters of judicial self-governance." Id., at 500. The Court has kept these two strands separate: "Article III standing, which enforces the Constitution's case-or-controversy requirement, see Lujan v. Defenders of Wildlife, 504 U.S. 555, 559–562 (1992); and prudential standing, which embodies 'judicially self-imposed limits on the exercise of federal jurisdiction,' Allen [v. Wright,] 468 U.S. [737,] 751 [(1984)]." Elk Grove Unified School Dist. v. Newdow, 542 U.S. 1, 11–12 (2004).

The requirements of Article III standing are familiar:


 * "First, the plaintiff must have suffered an 'injury in fact'—an invasion of a legally protected interest which is (a) concrete and particularized, and (b) 'actual or imminent, not "conjectural or hypothetical. Second, there must be a causal connection between the injury and the conduct complained of—the injury has to be 'fairly ... trace[able] to the challenged action of the defendant, and not ... th[e] result [of] the independent action of some third party not before the court.' Third, it must be 'likely,' as opposed to merely 'speculative,' that the injury will be 'redressed by a favorable decision. Lujan, supra, at 560–561 (footnote and citations omitted).

Rules of prudential standing, by contrast, are more flexible "rule[s] ... of federal appellate practice," ''Deposit Guaranty Nat. Bank v. Roper'', 445 U.S. 326, 333 (1980), designed to protect the courts from "decid[ing] abstract questions of wide public significance even [when] other governmental institutions may be more competent to address the questions and even though judicial intervention may be unnecessary to protect individual rights." Warth, supra, at 500.

In this case the United States retains a stake sufficient to support Article III jurisdiction on appeal and in