Apel, W. (1958). Gregorian chant. Indiana University Press.
Chicagoスタイル(17版)引用形式Apel, Willi. Gregorian Chant. Bloomington: Indiana University Press, 1958.
MLA(9版)引用形式Apel, Willi. Gregorian Chant. Indiana University Press, 1958.
警告: この引用は必ずしも正確ではありません.