@article{MABA_2001_15_1-2_a1,
     author = {V. T. Videv},
     title = {Two {Curvature} {Operators} in {Riemannian} and {Lorentzian} {Geometry}},
     journal = {Mathematica balkanica},
     pages = {7},
     publisher = {mathdoc},
     volume = {15},
     number = {1-2},
     year = {2001},
     url = {http://geodesic.mathdoc.fr/item/MABA_2001_15_1-2_a1/}
}