Sepper, M. M. (2007). Indirectal in Literary Estonian. Trames, 11(3), 299-323. https://www.airitilibrary.com/Article/Detail?DocID=17367514-200709-201011030039-201011030039-299-323
Engelbrecht, J., & Järv, J. (2013). Estonian Academy of Sciences 75. Proceedings of the Estonian Academy of Sciences, 62(4), 213-214. https://doi.org/10.3176/proc.2013.4.01