[1] G. Suñol: Text book of gregorian chant. (in English; also in French, German, Spanish and Italian). Desclée, Tournai 1930.

[2] P. Ferretti: Principii teoritici e pratici di Canto gregoriano. Rome 1933.

[3] A. Mocquereau: Le nombre musical grégorien ou rhythmique grégorienne. Tournai 1908 (Tom I), 1922 (Tom II).

[4] H. J. W. Tillyard: Handbook of the middle byzantine musical notation. Munksgaard, Copenhagen 1935.

[5] A. Salomaa: Formal languages. Academic Press, N. York-London 1973. MR 0438755 | Zbl 0262.68025

[6] Liber usualis missae et officii. Desclée, Tournai 1964.

[7] C. H. Lindsey S. G. van der Meulen: Informal introduction to ALGOL 68. North-Holland, Amsterdam-London 1971.