Henle catalogue. Level of difficulty The entire repertoire of G. Henle Verlag for piano solo (author: Rolf Koenen), violin (Ernst Schliephake) and flute (András Adorján) has been classified in difficulty levels from 1–9. Easy (1–3), Medium (4–6), Difficult (7–9). For example, the Prelude in C major from The Well-Tempered Clavier I has been classified as "moderately easy" (grade 2 out of 9), and the Toccata, Op. 7 by Robert Schumann as "very difficult" (9 out of 9). This classification is intended to make it easier to find suitable pieces for a particular level of ability. Special musicological publications and series Complete Editions Joseph Haydn Works, ed. Joseph Haydn-Institut Köln. Munich, since 1958ff. Musicological complete edition of Joseph Haydn's works.The edition, which is planned for 111 volumes, comprises 34 series. The edition is close to being completed. Ludwig van Beethoven: Works. Complete edition, ed. Beethoven-Archiv Bonn. Munich, since1961 (publications released by Beethoven-Hauses Bonn). The edition is planned for 56 volumes. Three quarters of these have been published so far. Johannes Brahms. New Edition of the Complete Works, ed. Johannes Brahms Gesamtausgabe, Munich, in conjunction with the Gesellschaft der Musikfreunde in Wien. Munich, since 1996.Historical-critical new edition of the complete compositional works of Johannes Brahms, with editorial management in Kiel. The edition is planned for 65 volumes in 10 series. Béla Bartók. BBCCE (Béla Bartók Complete Critical Edition), Munich (G. Henle Verlag) and Budapest (Editio Musica Budapest Zeneműkiadó), ed. Bartók-Archives of the Hungarian Academy of the Sciences. Since 2017. The edition is planned for 48 volumes and is trilingual (English, German, Hungarian; critical reports and footnotes in English only). Musicological books and series Ludwig van Beethoven Ludwig van Beethoven. Correspondence. Complete edition, ed. Sieghard Brandenburg, Munich 1996–1998. Volumes 1–6 cover letters from 1783 to 1827, volume 7 the index. Volume 8 (documents, subject index) is in preparation. Beethoven aus der Sicht seiner Zeitgenossen [Beethoven as seen by his contemporaries], ed. Klaus Martin Kopitz and Rainer Cadenbach, 2 vol., Munich 2009. Ludwig van Beethoven. Thematic Bibliographical Catalogue of Works, ed. by Kurt Dorfmüller, Norbert Gertsch and Julia Ronge with the additional support of Gertraut Haberkamp and the Beethoven-Haus Bonn, revised and significantly expanded new edition of the Catalogue of Works by Georg Kinsky and Hans Halm, Munich 2014. Johannes Brahms Johannes Brahms. Thematic Biliographical Catalogue of Works, ed. Margit L. McCorkle after conjunctual preparatory work with Donald McCorkle, Munich1984. Joseph Haydn Haydn-Studies. Publications