Cita APA (7a ed.)
Gunn, J. E., & Silverberg, R. This Fortress World. Ace Books.
Cita estilo Chicago (17a ed.)
Gunn, James E., y Robert Silverberg. This Fortress World. Nueva York, EUA: Ace Books.
Cita MLA (9a ed.)
Gunn, James E., y Robert Silverberg. This Fortress World. Ace Books.
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