Cita APA (7a ed.)

Apel, W. (1990). Gregorian chant. Indiana University Press.

Cita Chicago Style (17a ed.)

Apel, Willi. Gregorian Chant. Bloomington ; Indianapolis: Indiana University Press, 1990.

Cita MLA (9a ed.)

Apel, Willi. Gregorian Chant. Indiana University Press, 1990.