Task: songer_civproc1

What follows is an opinion from a United States Court of Appeals.
Your task is to identify the most frequently cited federal rule of civil procedure in the headnotes to this case. Answer "0" if no federal rules of civil procedure are cited. For ties, code the first rule cited.

PER CURIAM.
In the absence of an opinion by the district court, it is impossible for us to determine the basis of that court's decision in its denial of appellant’s petition for a writ of habeas corpus and to properly consider and pass upon the merits of
this appeal. Cf. United States ex rel. De-Vita v. McCorkle, 3 Cir., 1954, 216 F.2d 743.
The order of the district court will be vacated and the cause remanded for further proceedings in accordance with this opinion.

Question: What is the most frequently cited federal rule of civil procedure in the headnotes to this case? Answer with a number.
Answer:

Answer: 0