@article{10_4064_ap110_2_3,
     author = {Letizia Brunetti},
     title = {An {Osserman-type} condition on $g.f.f$-manifolds with {Lorentz} metric},
     journal = {Annales Polonici Mathematici},
     pages = {123--141},
     publisher = {mathdoc},
     volume = {110},
     number = {2},
     year = {2014},
     doi = {10.4064/ap110-2-3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap110-2-3/}
}