Geodesic
The signature of the Ricci curvature of left-invariant Riemannian metrics on four-dimensional Lie groups. The nonunimodular case
Matematičeskie trudy, Tome 12 (2009) no. 1, pp. 40-116 
A. G. Kremlyov; Yu. G. Nikonorov. The signature of the Ricci curvature of left-invariant Riemannian metrics on four-dimensional Lie groups. The nonunimodular case. Matematičeskie trudy, Tome 12 (2009) no. 1, pp. 40-116. http://geodesic.mathdoc.fr/item/MT_2009_12_1_a2/
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Voir la notice de l'article provenant de la source Math-Net.Ru

We obtain a complete classification of all the possible values of the signature of the Ricci curvature of left-invariant Riemannian metrics on four-dimensional nonunimodular Lie groups.

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