Nguyen, Doan Tuan, and Viet Duc Pham. “On the Degree of Holomorphic Mappings from an Annulus into an Annulus”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 8 (August 25, 2004): 1135–1138. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3828.