13.2. Art of Fugue, BWV 1080, various forms of the main subject: (a) from Contrapunctus 1, mm. 1–5; (b) inversion, from Contrapunctus 4, mm. 1–5; (c) version in dotted rhythm, from Contrapunctus 5, mm. 4–8; (d) inversion in dotted rhythm and rhythmic diminution, from Contrapunctus 6, mm. 2–4