  We show that every paracomplex space form is locally isometric to a modified
Riemannian extension and give necessary and sufficient conditions so that a
modified Riemannian extension is Einstein. We exhibit Riemannian extension
Osserman manifolds of signature (3,3) whose Jacobi operators have non-trivial
Jordan normal form and which are not nilpotent. We present new four dimensional
results in Osserman geometry.
