HIRST, L. Extending Singers. Contact: A Journal for Contemporary Music (1971-1990), [S. l.], n. 32, 1988. DOI: 10.25602/GOLD.cj.v0i32.1286. Disponível em: https://bjmh.gold.ac.uk/index.php/contactjournal/article/view/contactjournal32_p57-58. Acesso em: 27 may. 2024.