Can a defendant in a federal criminal trial receive for purposes of cross-examination any "statement" of the witness in the government's possession?

Under the Jencks Act a defendant in a federal criminal trial is entitled, after a government witness has testified on direct examination, to receive for purposes of cross-examination any "statement" of the witness in the government's possession "which relates to the subject matter as to which the witness has testified." 18 U.S.C. 3500(b) (1970). We have held that the statement must at least "relate generally to the events and activities testified to" before the statement must be produced, United States v. Cardillo, 316 F.2d 606, 615 (2d Cir.), cert. denied, 375 U.S. 822, 84 S.Ct. 60, 11 L.Ed.2d 55 (1963), and that the defense is not entitled to statements which are merely "incidental or collateral." United States v. Birnbaum, 337 F.2d 490 (1964). On the other hand, where the government's representations as to relevancy are challenged, the better practice is for it to make the disputed statement available to the trial judge for an in camera inspection and ruling, which will normally be upheld in the absence of a showing of abuse of discretion, see, e. g., United States v. Covello, 410 F.2d 536 (2d Cir. 1969), cert. denied, 396 U.S. 879, 90 S.Ct. 150, 24 L.Ed.2d 136, rehearing denied, 397 U.S. 929, 90 S.Ct. 897, 25 L.Ed.2d 110 (1970), rather than risk reversal of a conviction because it played its cards too close to the vest. See United States v. Borelli, 336 F.2d 376, 393 (2d Cir.), cert. denied, 379 U.S. 960, 85 S.Ct. 647, 13 L.Ed.2d 555 (1964).