On a certain application of Patterson's curvature identity

We present curvature properties of four-dimensional semi-Riemannian manifolds satisfying some condition of pseudosymmetry type. We prove that every such manifold with non-zero associated function L is pseudosymmetric, its scalar curvature does not vanish and L must be equal to 1/3. We also describe non-trivial example of a manifold realizing all these coditions.