 Such "nested proportions", as Cage called them, became a regular feature of his music throughout the 1940s.The technique was elevated to great complexity in later pieces such as "Sonatas and Interludes" for prepared piano (1946–48), in which many proportions used non-integer numbers (1¼, ¾, 1¼, ¾, 1½, and 1½ for "Sonata I", for example), or "A Flower", a song for voice and closed piano, in which two sets of proportions are used simultaneously.In late 1940s, Cage started developing further methods of breaking away with traditional harmony.