Ổn, Phùng Văn. “on the Complexity of Recognition of Regular Layer Languages Generating by Extended Hyper Generating-Schemas”. Journal of Computer Science and Cybernetics 20, no. 2 (July 25, 2012): 176–182. Accessed May 2, 2024. https://vjs.ac.vn/index.php/jcc/article/view/1474.