dissenting.
There can be no doubt that the problem in this case is a problem of federalism. Competing considerations of the greatest significance are involved. But in resolving questions that touch upon the intricate and delicate mechanism of our federal system it is especially important to remember, as Mr. Justice Holmes observed, that “General propositions do not decide concrete cases.” Lochner v. New York, 198 U. S. 45, 76. In this case the New York courts sustained petitioner’s conviction on the under*382standing that in the circumstances of this case the testimony petitioner was compelled to give before the New York State grand jury could not, as a matter of federal law, be employed in a subsequent federal prosecution. On the other hand, it is implicit in the majority opinion in this Court that the petitioner does run the risk of a federal prosecution based on his own testimony under Feldman v. United States, 322 U. S. 487. If we are to have any profitable discussion of federalism based on the facts of this case, we should begin with agreement on the facts and the controlling principles. In any event, we should not affirm a New York conviction if in fact the state courts construed state law under a misconception of federal law. To do so does violence to the vital principle of federalism that a state court is the final arbiter of state law. See May v. Anderson, 345 U. S. 528, 534, 535. I therefore agree with Mr. Justice Black that this case should be remanded so that the New York Court of Appeals can reconsider state law in light of the majority’s conclusion that the role of the federal prosecutor was not such as to prevent use of the state-compelled testimony against petitioner in a federal prosecution. At all events, the unsettling influence that Feldman has had upon the course of this litigation indicates that a satisfactory solution cannot be reached without a reconsideration of that decision.