Phutphong Thongrat. 1988. A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces. Faculty of Graduate Studies, Mahidol University;
Phutphong Thongrat. (1988) A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces . Mahidol University/Bangkok.
Phutphong Thongrat. A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces. . Bangkok:Mahidol University, 1988.
Phutphong Thongrat. (1988) A comparative phonological study of Thai Phuan at Suphanburi and Sukhothai provinces . Mahidol University/Bangkok.