Chao, Yuen-Ren 1934: The non-uniqueness of phonemic solutions of phonetic systems. Bulletin of the Institute of History and Philology, Academia Sinica IV: 4: 363–397. Julkaistu myös teoksessa Martin Joos (toim.): Readings in linguistics: The development of descriptive linguistics in America since 1925. Toinen laitos. American Council of Learned Societies, New York 1958. Löytyy vapaasti verkosta: https://archive.org/details/readingsinlingui00joos
