⁸  Elena Toncheva. ‘The Bulgarian Liturgical Chant...’, p. 142.; Svetlana Kujumdzhieva, Стара Българска Музика [trans Old Bulgarian Music], (in Bulgarian), (Sofia: Mars 09, 2011), p.47.; Svetlana Poliakova. ‘Russian Liturgical Chant Books from the 11th-14th Centuries and Their Function in Liturgical Practice’, Medieval Sacred Chant: from Japan to Portugal. Canto sacro medieval: do Japão a Portugal, ed. Ferreira M.P., Lisbon, 2008, pp. 93-111.