Authors: D. Catalano Ferraioli and A. M. Vinogradov

Pseudo-Riemannian 4-metrics with bidimensional null Killing orbits are studied. Both Lorentzian and Kleinian (or neutral) cases, are treated simultaneously. Under the assumption that the distribution orthogonal to the orbits is completely integrable a complete exact description of Ricci flat metrics admitting a bidimensional nonabelian Killing algebra is found.

17 pages, AmS-LaTeX (LaTeX-2e).

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