Mr. Chief Justice Burger, concurring.
I join the opinion of the Court but I add a word about the composition of the three-judge District Court and the circumstances under which it was convened. Under 28 U.S.C. §2284(1) the district judge to whom the application for relief is presented, and who notifies the chief judge of the need to convene the three-judge court, "shall constitute one member of such court." It is well settled that "shall" means "must," cf. Merced Rosa v. Herrero, 423 F.2d 591, 593 n. 2 (CA1 1970), yet the judge who called for the three-judge court here was not named to the panel. However, appellants made no timely objection to the composition of the court. Ante, at 338 n. 5. Obviously occasions can arise rendering it impossible for the district judge who initiates the convening of such a court under §2284(1) to serve on the court, but, in light of the unqualified mandatory language of the statute, when that occurs there is an obligation to [p. 353] see to it that the record reveal, at the very least, a statement of the circumstances accounting for the substitution.