▁end ▁of ▁the ▁ 1 2 th ▁and ▁beginning ▁of ▁the ▁ 1 3 th ▁century ▁and ▁is ▁pres umed ▁to ▁have ▁been ▁French . ▁The ▁only ▁definit ive ▁information ▁on ▁his ▁life ▁comes ▁from ▁a ▁brief ▁mention ▁attributed ▁to ▁the ▁musical ▁the or ist ▁Johannes ▁de ▁Gar land ia ▁( fl . c . 1 2 7 0 – 1 3 2 0 ) ▁in ▁his ▁De ▁Mens ur ab ili ▁Mus ica , ▁and ▁four ▁references ▁in ▁the ▁works ▁of ▁an ▁English ▁student , ▁known ▁today ▁as ▁An onymous ▁IV , ▁including ▁this , ▁most ▁commonly ▁c ited ▁paragraph ; ▁These ▁rules ▁were ▁used ▁in ▁many ▁older ▁books ; ▁this ▁was ▁so ▁during ▁and ▁after ▁the ▁time ▁of ▁Per ot inus ▁the ▁Great . ▁Nevertheless , ▁they ▁did ▁not ▁know ▁how ▁to ▁distinguish ▁these ▁notes ▁from ▁those ▁which ▁will ▁be ▁presented ▁shortly . ▁This ▁was ▁so ▁even ▁since ▁the ▁time ▁of ▁Leo , ▁because ▁two ▁lig ated ▁notes ▁were ▁put ▁for ▁the ▁dur ational ▁value ▁of ▁a ▁bre vis ▁long a , ▁and ▁in ▁a ▁similar ▁manner , ▁three ▁lig ated ▁notes ▁were ▁quite ▁often ▁used ▁for ▁a ▁long a ▁bre vis , ▁long a . ▁People ▁say ▁Ma ître ▁Leon in ▁was ▁the ▁best ▁composer ▁of ▁Organ um ▁( optim us ▁organ ista ), ▁he ▁composed ▁the ▁Great ▁Organ um ▁Book ▁for ▁the ▁grad ual ▁and ▁anti phon ary ▁in ▁order ▁to ▁prolong ▁the ▁divine ▁service . ▁This ▁book ▁remained ▁in ▁use ▁until ▁the ▁time ▁of ▁the ▁great ▁Per ot