Some Hypersurfaces with Constant Mean Curvature in a Conformally Flat Riemannian Manifold

§1. T. Otsuki [1] studied the minimal hypersurface Vof a Riemannian manifold Sof constant curvature if the number of the distinct principal normal curvatures is two and the multiplicities of them are at least two. He proved that Vis locally the Riemannian prodruct S×Sof two Riemannian manifolds Sand Sof constant curvature, where ιand ιare these multiplicities, respectively. In the present paper Sdenotes an m-dimensional Riemannian manifold of