In California v. Green (1970) 399 U.S. 149, the high court held that admission at trial of a witness's prior inconsistent statements did not violate the defendant's confrontation clause rights because the witness actually testified and was subject to cross-examination about his out-of-court statements. (Green, supra, 399 U.S. at pp. 164, 168.) The court identified the purposes of confrontation as: "(1) insuring that the witness will give his statements under oath--thus impressing him with the seriousness of the matter and guarding against the lie by the possibility of a penalty for perjury; (2) forcing the witness to submit to cross-examination, the 'greatest legal engine ever invented for the discovery of truth'; and (3) permiting the jury that is to decide the defendant's fate to observe the demeanor of the witness in making his statement, thus aiding the jury in assessing his credibility." (Id. at p. 158.) The court noted that "a narrow question lurking" in the case was whether the witness's "apparent lapse of memory so affected the defendant's right to cross-examine as to make a critical difference in the application of the Confrontation Clause," but the majority concluded the issue was not yet ripe for decision. (Id. at pp. 168-169.) In his concurring opinion in Green, Justice Harlan addressed that lurking question. "The fact that the witness, though physically available, cannot recall either the underlying events that are the subject of an extra-judicial statement or previous testimony or recollect the circumstances under which the statement was given, does not have Sixth Amendment consequence. The prosecution has no less fulfilled its obligation simply because a witness has a lapse of memory. The witness is, in my view, available. To the extent that the witness is, in a practical sense, unavailable for cross-examination on the relevant facts, . . . I think confrontation is nonetheless satisfied." (Green, supra, 399 U.S. at pp. 188-189, fn. omitted (conc. opn. of Harlan, J.).)