↑ Terry E. Miller, Sean Williams(2008).The Garland handbook of Southeast Asian music.Routledge.p.262.ISBN0-415-96075-4
↑ Songs for the Spirits: Music and Mediums in Modern Vietnam p150 Barley Norton - 2009 "These include the ca tru pieces “Ty Ba Hanh” and “Bac Phan,” which became part of the “Phu” group of songs and were .