The most celebrated book on counterpoint is Fux's great theoretical work Gradus ad Parnassum. Since its appearance in 1725, it has been used by and has directly influenced the work of many of the greatest composers. J.S. Bach held it in high esteem, Leopold Mozart trained his famous son from its pages, Haydn worked out every lesson with meticulous care, and Beethoven condensed it into an abstract for ready reference.