Spacelike surfaces which admit a nondegenerate null normal section in a Lorentzian space form Fuente Benito, Daniel de la Palomo, Francisco J. Romero Sarabia, Alfonso Spacelike surface Gauss curvature Liebmann theorem In this paper, we develop a formula for spacelike surfaces in a 4- dimensional Lorentzian space form which involves its mean curvature vector eld and the Gauss curvature of the induced metric and the Gauss curvature of the second fundamental form associated to a non- degenerate null normal section. By means of this formula, we stablish several su cient conditions for compact spacelike surfaces with con- stant Gauss curvature to have a null umbilical direction. As another application, we give a new proof of the Liebmann rigidity theorem in Euclidean, hemispherical and hyperbolic spaces, and in the De Sitter spacetime. 2024-03-18T12:01:07Z 2024-03-18T12:01:07Z 2019 info:eu-repo/semantics/article Publisher version: de la Fuente, D., Palomo, F.J. & Romero, A. On Non-degenerate Null Normal Sections of Codimension Two Spacelike Surfaces. Bull. Malays. Math. Sci. Soc. 42, 1451–1467 (2019). https://doi.org/10.1007/s40840-017-0557-x https://hdl.handle.net/10481/90079 10.1007/s40840-017-0557-x eng http://creativecommons.org/licenses/by-nc-nd/4.0/ info:eu-repo/semantics/openAccess Attribution-NonCommercial-NoDerivatives 4.0 Internacional