who is credited with compiling the great book of organum (magnus liber organi)
Magnus Liber The Magnus Liber or Magnus Liber Organi (Latin for "Great Book of Organum") is a compilation of the medieval music known as organum. The whole name of the work is Magnus liber organi de graduali et antiphonario pro servitio divino. Written during the 12th and early 13th centuries, this series of compositions is attributed to masters of the Notre Dame school of music, most notably Léonin and his successor Pérotin. (These names survive today because of the testimony of an English music theorist known simply as Anonymous IV.)