21. It was Max Unger who suggested a connection between the writing out of these cadenzas and the painstaking preparation of theoretical abstracts for the teaching of the Archduke, enterprises undertaken beginning in May 1809 during those chaotic months of the siege and occupation of Vienna, a period not conducive to the true work of composition. But Beethoven did compose: Opera 73, 73, 78, 81a, 84 (Egmont), and 95 all date from 1809–1810. Unger expressed his views in a personal communication to Ludwig Misch, who conveyed them in his Beethoven Studies (Norman: University of Oklahoma Press, 1953), 176–177, n. 8.