Count taken from Graham Parkes, "The symphonic structure of Also sprach Zarathustra: a preliminary outline", in Luchte, James (2011). Nietzsche's Thus Spoke Zarathustra: Before Sunrise. Bloomsbury Publishing. ISBN978-1441118455.. Excerpts online at [1].
The conjecture about the child Mozart's three-movement preference is made by Gärtner, who notes that Mozart's father Leopold and other older composers already preferred four. See Gärtner, Heinz (1994). John Christian Bach: Mozart's Friend and Mentor. Hal Leonard Corporation. ISBN0931340799. Excerpts online at [2].
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