Koestler, A., & Butterfield, H. (1964). The Sleepwalkers: A history of man's changing vision of the universe; with an introduction by Herbert Butterfield. Penguin.
Chicago-viite (17. p.)Koestler, Arthur, ja Herbert Butterfield. The Sleepwalkers: A History of Man's Changing Vision of the Universe; with an Introduction by Herbert Butterfield. London: Penguin, 1964.
MLA-viite (9. p.)Koestler, Arthur, ja Herbert Butterfield. The Sleepwalkers: A History of Man's Changing Vision of the Universe; with an Introduction by Herbert Butterfield. Penguin, 1964.
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