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In page Pérotin:

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Anonymous IV identified seven works, that he presumably considered worthy of singling out, and these represent the only direct attribution. Subsequent authors have attributed works on stylistic and chronological grounds. These include Friedrich Ludwig (1910),[1] Heinrich Husmann (1940),[2] Hans Tischler (1950)[3] and Ethel Thurston (1970).[4] Husmann added an additional nine three-part organa, and five clausula to which Ludwig added numerous other clausula.[5] Other authors have attributed all the three-part organa in the Magnus Liber to Pérotin, which is unlikely. Nevertheless, two of the only three known four-part organa can be attributed to him.[3]