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Published online by Cambridge University Press: 30 September 2008
Locally 2+2 warped product metrics with a Lorentzian base andRiemannian fiber are described in Newman-Penrose formalism. Itis shown that solutions with rank-1 Ricci tensor arecharacterized by Φ11 + 3Λ = 0 and Φ00Φ22 = (Φ11-3Λ)2. Integrabilityconditions for the Bianchi identities are studied and it isproved that the sources are null Einstein-Maxwell fields,massless scalar fields or stiff matter fields correspondingrespectively to Λ = 0, Λ > 0 or Λ < 0.