Weera Ostapirat. (1993) Proto-Hlai vowel system. Mahidol University,:ม.ป.ท.Weera Ostapirat. 1993. Proto-Hlai vowel system. ม.ป.ท.:Mahidol University,;Weera Ostapirat. Proto-Hlai vowel system. ม.ป.ท.:Mahidol University, 1993. Print.