TY  - JOUR
AU  - A. G. Kremlyov
AU  - Yu. G. Nikonorov
TI  - The signature of the Ricci curvature of left-invariant Riemannian metrics on four-dimensional Lie groups. The unimodular case
JO  - Matematičeskie trudy
PY  - 2008
SP  - 115
EP  - 147
VL  - 11
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MT_2008_11_2_a3/
LA  - ru
ID  - MT_2008_11_2_a3
ER  -