, ▁disc ant us , ▁style , ▁the ▁ten or ▁was ▁allowed ▁to ▁be ▁mel ism atic , ▁and ▁the ▁notes ▁were ▁quick er ▁and ▁more ▁regular ▁with ▁the ▁upper ▁part ▁becoming ▁equally ▁rh yth mic . ▁These ▁more ▁rh yth mic ▁sections ▁were ▁known ▁as ▁cla us ula e ▁( p unct a ). ▁Another ▁innov ation ▁was ▁the ▁standard ization ▁of ▁note ▁forms , ▁and ▁Lé on in ' s ▁new ▁square ▁notes ▁were ▁quickly ▁adopted . ▁Although ▁he ▁developed ▁the ▁disc ant us ▁style , ▁Lé on in ' s ▁strength ▁was ▁as ▁a ▁writer ▁of ▁organ um ▁pur um . ▁The ▁singing ▁of ▁org ana ▁fell ▁into ▁dis use ▁by ▁the ▁mid ▁th ir teenth ▁century . ▁Associ ated ▁with ▁the ▁Notre ▁D ame ▁school , ▁was ▁Johannes ▁de ▁Gar land ia , ▁whose ▁De ▁mens ur ab ili ▁provided ▁a ▁theoretical ▁basis , ▁for ▁Notre ▁D ame ▁poly phony ▁is ▁essentially ▁musica ▁mens ur abil is , ▁music ▁that ▁is ▁measured ▁in ▁time . ▁ ▁In ▁his ▁treat ise , ▁he ▁defines ▁three ▁forms ▁of ▁poly phony , ▁organ um ▁in ▁special i , ▁cop ula , ▁and ▁disc ant , ▁which ▁are ▁defined ▁by ▁the ▁relationship ▁of ▁the ▁voices ▁to ▁each ▁other ▁and ▁by ▁the ▁rh yth mic ▁flow ▁of ▁each ▁voice . ▁ ▁Magn us ▁liber ▁organ i ▁▁ ▁Lé on in ▁compiled ▁his ▁compos itions ▁into ▁a ▁book , ▁the ▁Magn us ▁liber ▁organ i ▁( Gre at ▁Organ um ▁Book ), ▁around ▁ 1