We study semi-parallel lightlike hypersurfaces of an indefinite
Kenmotsu manifold, tangent to the structure vector field. Some Theorems
on parallel and semi-parallel vector field, geodesibility of lightlike
hypersurfaces ...

We investigate lightlike hypersurfaces of indefinite Sasakian manifolds,
tangent to the structure vector field and whose screen distribution is
integrable. We prove some results on parallel vector fields and on a leaf ...