Song Hyon's "Model for Study of Music" (Akhak kwebom) and the historical development of the Neo-Confucian concept of music in fifteenth-century Chosen Korea, with translations of the "Introduction" to the "Model for Study of Music" and excerpts from the "Investigation of Music" (Akko) in the late Choson "Reference Compilation of Documents on Korea" (Chungbo munhon pigo)