▁disc ant ▁composition ., ▁In ▁the ▁original ▁disc ant ▁organ um ▁du pl um , ▁the ▁second ▁voice ▁follows ▁the ▁cant us ▁firm us , ▁note ▁on ▁note ▁but ▁at ▁an ▁interval , ▁usually ▁a ▁fourth ▁above . ▁By ▁contrast , ▁in ▁the ▁flor id ▁organ um , ▁the ▁upper ▁or ▁vo x ▁organ alis ▁voice ▁w ove ▁shorter ▁notes ▁around ▁the ▁longer ▁notes ▁of ▁the ▁lower ▁ten or ▁chant . ▁ ▁P é rot in ' s ▁compos itions ▁▁ ▁An onymous ▁IV ▁mentions ▁a ▁number ▁of ▁compos itions ▁which ▁he ▁attributes ▁to ▁P é rot in , ▁including ▁the ▁four - voice ▁V ider unt ▁om nes ▁and ▁S eder unt ▁princip es , ▁and ▁the ▁three - voice ▁Alle lu ia ▁" Pos ui ▁ad i utor ium " ▁and ▁Alle lu ia ▁" N ativ itas ". ▁Johannes ▁de ▁Gar land ia ▁states ▁that ▁the ▁Magn us ▁Liber ▁comm ences ▁with ▁Per ot in ' s ▁four - part ▁org ana , ▁and ▁makes ▁specific ▁reference ▁to ▁the ▁notation ▁in ▁the ▁three - part ▁Alle lu ya , ▁Pos ui ▁ad i utor ium . ▁Other ▁works ▁are ▁attributed ▁to ▁him ▁by ▁later ▁sch ol ars , ▁such ▁as ▁Heinrich ▁Hus mann , ▁on ▁sty list ic ▁grounds , ▁all ▁in ▁the ▁organ um ▁style , ▁as ▁well ▁as ▁the ▁two - voice ▁Dum ▁sig ill um ▁sum mi ▁Pat ris ▁and ▁the ▁mon oph onic ▁Be ata ▁vis cera ▁in ▁the ▁conduct us ▁style . ▁( The ▁conduct