Totally umbilical lightlike submanifolds (Q1420220)

In the paper under review the authors study the geometry of totally umbilical light-like submanifolds. First they recall some results for light-like submanifolds and their structure equations. Next they prove several new theorems on such submanifolds in semi-Riemannian manifolds of constant curvature. The authors show that the induced Ricci tensor of any totally umbilical light-like submanifold in a manifold of constant curvature is symmetric if and only if its screen distribution is integrable. It is worth noticing that many well-known spacetimes have light-like hypersurfaces with an integrable 2-dimensional screen distribution.