Ramamurthy, Bina, Vũ Nghĩa, and Vũ Đức Thi. “On the Direct Product of Choice Function”. <i>Journal of Computer Science and Cybernetics</i> 18, no. 3 (July 29, 2012): 290–299. Accessed January 13, 2026. https://vjes.vast.vn/jcc/article/view/1593.