Repovš, D., and V. V. Sharko. “$S^1$-Bott Functions on Manifolds”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 12 (December 25, 2012): 1685–1698. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/2691.