Phutphong Thongrat. (1988) A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces. Mahidol University,:ม.ป.ท.Phutphong Thongrat. 1988. A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces. ม.ป.ท.:Mahidol University,;Phutphong Thongrat. A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces. ม.ป.ท.:Mahidol University, 1988. Print.