sry
https://twitter.com/Andy5x5/status/1263203597132718080
The D.C. Circuit Court is merely following
Federal Rules of Appellate Procedure, Rule 21 "Writs of Mandamus and Prohibition, and Other Extraordinary Writs", Section (b)(1), as follows:
Rule 21. Writs of Mandamus and Prohibition, and Other Extraordinary Writs
(a) Mandamus or Prohibition to a Court: Petition, Filing, Service, and Docketing.
(1) A party petitioning for a writ of mandamus or prohibition directed to a court must file a petition with the circuit clerk and serve it on all parties to the proceeding in the trial court. The party must also provide a copy to the trial-court judge. All parties to the proceeding in the trial court other than the petitioner are respondents for all purposes.
(2)(A) The petition must be titled “In re [name of petitioner].”
(B) The petition must state:
(i) the relief sought;
(ii) the issues presented;
(iii) the facts necessary to understand the issue presented by the petition; and
(iv) the reasons why the writ should issue.
(C) The petition must include a copy of any order or opinion or parts of the record that may be essential to understand the matters set forth in the petition.
(3) Upon receiving the prescribed docket fee, the clerk must docket the petition and submit it to the court.
(b) Denial; Order Directing Answer; Briefs; Precedence.
(1) The court may deny the petition without an answer.
Otherwise, it must order the respondent,
if any, to answer within a fixed time.
(2) The clerk must serve the order to respond on all persons directed to respond.
(3) Two or more respondents may answer jointly.
(4) The court of appeals may invite or order the trial-court judge to address the petition or may invite an amicus curiae to do so. The trial-court judge may request permission to address the petition but may not do so unless invited or ordered to do so by the court of appeals.
(5) If briefing or oral argument is required, the clerk must advise the parties, and when appropriate, the trial-court judge or amicus curiae.
(6) The proceeding must be given preference over ordinary civil cases.
(7) The circuit clerk must send a copy of the final disposition to the trial-court judge.
***
https://www.law.cornell.edu/rules/frap/rule_21
I should have added that this is a threshold first win for Gen. Flynn as the Court could have "denied the petition without an answer". Instead, the Court has deemed the issue joined and Judge Sullivan now has a lot of 'plaining to do in convincing the D.C. Court of Appeals just why it shouldn't grant Gen. Flynn's Petition. The stage is now set for the public humiliation and further exposure of a weaponized IC, FBI and, perhaps now, a Federal District Court.