BavulaV. V. “Extreme Modules over the Weyl Algebra $A_n$”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 9 (September 25, 1993): 1187-1197. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5920.