Zelazny, R. (1967). Four for tomorrow. Ace Books.
Cita Chicago (17th ed.)Zelazny, Roger. Four for Tomorrow. New York: Ace Books, 1967.
Cita MLA (9th ed.)Zelazny, Roger. Four for Tomorrow. Ace Books, 1967.
Atenció: Aquestes cites poden no estar 100% correctes.