A topological proof of the Arnold four cusps theorem
\textit{V. I. Arnold} in [Rev. Mat. Univ. Complutense Madr. 8, No. 1, 109--119 (1995; Zbl 0973.53501)] proved a theorem stating that on a generic Riemannian surface which is sufficiently close to a sphere has at least four semi-cubical vertices. The author proves the same fact using the Morse theory and replacing the condition of closeness to the sphere by some less restrictive geometric hypothesis.
scientific article; zbMATH DE number 6064188