Jaratjarungkiat, S., Park, K.-E., Pichetpan, N., & Tan, S. Y. H. (2023). The Grammaticalization of the Copulas /pēn/ and /kʰɯ̄ ː/ in Thai. Journal of Mekong Societies, 19(2), 92–119. retrieved from https://so03.tci-thaijo.org/index.php/mekongjournal/article/view/266198