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Examples of Osserman pseudo-Riemannian manifolds with metric of any signature (p, q), p, q > 1 which are not locally symmetric are exhibited.

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Three-dimensional Lorentzian manifolds with commuting curvature operators are studied. A complete description is given at the algebraic level. Consequences are obtained at the differentiable setting for manifolds which additionally are assumed to be locally symmetric or homogeneous.