Kull, Kalevi, and Ekaterina Velmezova. “What Is the Main Challenge for Contemporary Semiotics?”. Sign Systems Studies 42, no. 4 (December 31, 2014): 530-548. Accessed August 17, 2022. http://ojs.utlib.ee/index.php/sss/article/view/SSS.2014.42.4.06.