Farber, M. (2002) “Zeros of closed 1-forms, homoclinic orbits and Lusternik-Schnirelman theory”, Topological Methods in Nonlinear Analysis, 19(1), pp. 123–152. Available at: https://apcz.umk.pl/TMNA/article/view/TMNA.2002.008 (Accessed: 28 March 2024).