@article{10_4153_CJM_2006_012_1,
     author = {Fels, M. E. and Renner, A. G.},
     title = {Non-reductive {Homogeneous} {Pseudo-Riemannian} {Manifolds} of {Dimension} {Four}},
     journal = {Canadian journal of mathematics},
     pages = {282--311},
     year = {2006},
     volume = {58},
     number = {2},
     doi = {10.4153/CJM-2006-012-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-2006-012-1/}
}