Topological rigidity for closed hypersurfaces of elliptic space forms

We prove a topological rigidity theorem for closed hypersurfaces of the Euclidean sphere and of an elliptic space form. It asserts that, under a lower bound hypothesis on the absolute value of the principal curvatures, the hypersurface is diffeomorphic to a sphere or to a quotient of a sphere by a group action. We also prove another topological rigidity result for hypersurfaces of the sphere that involves the spherical image of its usual Gauss map.

Galois Lines for Normal Elliptic Space Curves, II

For each linearly normal elliptic curve C ⊂ ℙ3, we determine Galois lines and their arrangement. We prove that the curve C has exactly six V4-lines. In case j(C) = 1, it has eight Z4-lines in addition. The V4-lines form the edges of a tetrahedron. In case j(C) = 1, for each vertex of the tetrahedron, there exist exactly two Z4-lines passing through it. As a corollary we obtain that each plane quartic curve of genus 1 does not have more than one Galois point.