Weera Ostapirat. 1993. Proto-Hlai vowel system. Faculty of Graduate Studies, Mahidol University;
Weera Ostapirat. (1993) Proto-Hlai vowel system . Mahidol University/Bangkok.
Weera Ostapirat. Proto-Hlai vowel system. . Bangkok:Mahidol University, 1993.
Weera Ostapirat. (1993) Proto-Hlai vowel system . Mahidol University/Bangkok.