Other writers who covered the topic of rhythmic modes include Anonymous IV, who mentions the names of the composers Léonin and Pérotin as well as some of their major works, and Franco of Cologne, writing around 1260, who recognized the limitations of the system and whose name became attached to the idea of representing the duration of a note by particular notational shapes, though in fact the idea had been known and used for some time before Franco . Lambertus described nine modes, and Anonymus IV said that, in England, a whole series of irregular modes was in use .