Martínez-Alfaro, J., Meza-Sarmiento, I. S., & Oliveira, R. D. S. (2018). Singular levels and topological invariants of Morse--Bott foliations on non orientable surfaces. Topological Methods in Nonlinear Analysis, 51(1), 183–213. Retrieved from https://apcz.umk.pl/TMNA/article/view/TMNA.2017.051