@article{10_5817_AM2014_3_171,
     author = {Guediri, Mohammed and Bin-Asfour, Mona},
     title = {Ricci-flat left-invariant {Lorentzian} metrics on 2-step nilpotent {Lie} groups},
     journal = {Archivum mathematicum},
     pages = {171--192},
     publisher = {mathdoc},
     volume = {50},
     number = {3},
     year = {2014},
     doi = {10.5817/AM2014-3-171},
     mrnumber = {3263659},
     zbl = {06487005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5817/AM2014-3-171/}
}