Editing Opus number (section)

==Early usage==
In the arts, an opus number usually denotes a work of [[musical composition]], a practice and usage established in the seventeenth century when composers identified their works with an opus number. In the eighteenth century, publishers usually assigned opus numbers when publishing groups of like compositions, usually in sets of three, six or twelve compositions. Consequently, opus numbers are not usually in chronological order, unpublished compositions usually had no opus number, and numeration gaps and sequential duplications occurred when publishers issued contemporaneous editions of a composer's works, as in the sets of [[string quartet]]s by [[Joseph Haydn]] (1732–1809) and [[Ludwig van Beethoven]] (1770–1827); Haydn's Op. 76, the [[String Quartets, Op. 76 (Haydn)|Erdödy quartets]] (1796–97), comprises six discrete quartets consecutively numbered Op. 76 No. 1&nbsp;– Op. 76 No. 6; whilst Beethoven's Op. 59, the [[String Quartets Nos. 7–9, Op. 59 – Rasumovsky (Beethoven)|Rasumovsky quartets]] (1805–06), comprises String Quartet No. 7, String Quartet No. 8, and String Quartet No. 9.