@article{SIGMA_2010_6_a4,
     author = {Giovanni Calvaruso and Eduardo Garc{\'\i}a-R{\'\i}o},
     title = {Algebraic {Properties} of {Curvature} {Operators} in {Lorentzian} {Manifolds} with {Large} {Isometry} {Groups}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2010},
     volume = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2010_6_a4/}
}