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Source
Reti, Rudolph (1958). Tonality, Atonality, Pantonality: A study of some trends in twentieth century music. Westport, Connecticut: Greenwood Press. ISBN 0313204780.
Bitonality was used quite often by members of the French group, Les Six, and especially by Darius Milhaud, who perhaps used it more than any other composer.
Although the word bitonality is most often used when talking about relatively modern classical music (written in the last one hundred years or so), it is quite a common technique in folk music, especially in eastern Europe.
Bartók also uses the white-key and fl-key collections (diatonic scale and its penatonic complement) in no.6 of the Eight Improvisations, with the pentatonic as foreground, and in mm.50-51 of the third movement of his Fourth Quartet, with the diatonic as foreground.