YEN, CHEN-TE. “ON RINGS SATISFYING BOTH OF 1-Abc AND 1-Cba BEING INVERTIBLE OR NONE”. Tamkang Journal of Mathematics 24, no. 3 (September 1, 1993): 317–321. Accessed July 5, 2022. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4503.