Cita APA (7th ed.)
Hempel, C. G. Philosophy of Natural Science. Prentice-Hall.
Cita Chicago (17th ed.)
Hempel, Carl G. Philosophy of Natural Science. Englewood Cliffs, EUA: Prentice-Hall.
Cita MLA (9th ed.)
Hempel, Carl G. Philosophy of Natural Science. Prentice-Hall.
Atenció: Aquestes cites poden no estar 100% correctes.