GYOVAI, Ágnes, and Tímea Mária HEVESI. “THE CIRCLE SYMBOL IN MUSIC EDUCATION”. Studia Universitatis Babeș-Bolyai Musica, vol. 60, no. 2, Dec. 2015, pp. 95-107, https://studia.reviste.ubbcluj.ro/index.php/subbmusica/article/view/5098.