Monreale, Il Duomo, Una formella da i battenti bronzei, opera firmata di Bonanno Pisano (ca. 1186)

Johannes Monachus to Extravag. com. 2.3.1 (Rem non novam) v. Non obstantibus aliquibus privilegiis: 

Necesse est ipsum citari et uocari; nec papa hoc potest omittere, et minus alius iudex, quia sic omitteretur cognitio que ad iudicium de necessitate requiritur . . . Et sic patet secundum et tertium simul, scilicet quod citatio est de iure naturali et per consequens quod papa contra aliquem procedere non potest nisi citatione premissa. (It is necessary that the Defendant (reus) be cited and summoned.  The pope may not omit this, and even less another judge.  If the summons would be omitted <it would be wrong> because it is required by necessity.  The summons is a part of natural law (ius) and and consequently the pope cannot proceed without summoning the defendant (reus)).