Sumner v. Mata, 455 U.S. 591, 591-92, 597 (1982) (We agree with the Court of Appeals that the ultimate question as to the constitutionality of the pretrial identification procedures used in this case is a mixed question of law and fact that is not governed by 2254(d), which requires federal courts in habeas proceedings to accord a presumption of correctness to state-court findings of fact.); S