Pratchett, T. (1988). Wyrd systems. Corgi Books.
Cita Chicago (17th ed.)Pratchett, Terry. Wyrd Systems. London: Corgi Books, 1988.
Cita MLA (8th ed.)Pratchett, Terry. Wyrd Systems. Corgi Books, 1988.
Atenció: Aquestes cites poden no estar 100% correctes.