Publicationes Mathematicae, cilt.58, sa.4, ss.587-604, 2001 (SCI-Expanded)
In the paper we prove that under some additional curvature condition the relations R · R = 0 and R · S = 0 are equivalent for hypersurfaces of semi-Euclidean spaces. We present also examples of hypersurfaces having the curvature tensor expressed by the square, in the sense of the Kulkarni - Nomizu product, of the Ricci tensor.