T. V. Budnyts'ka and O. O. Prishlyak, “Equivalence of closed 1-forms on surfaces with edge”, Ukr. Mat. Zhurn., vol. 61, no. 11, pp. 1455–1473, Nov. 2009, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3114