Johannes Monachus to Extravag. com. 2.3.1 (Rem non novam) v. Non obstantibus aliquibus privilegiis:
It is necessary to summon and cite the defendant. Even the pope may not omit the summons, and even less another judge may not omit a summons because necessity demands it . . . The summons is based on natural law. Consequently the pope cannot bring someone to trial without a summons.