@article{MZ_1971__119_171500,
     author = {Grigorios Tsagas},
     title = {Some {Properties} of the {Curvature} {Operator} of a {Riemannian} {Manifold.}},
     journal = {Mathematische Zeitschrift},
     pages = {283--286},
     publisher = {mathdoc},
     volume = {119},
     year = {1971},
     zbl = {0195.23503},
     url = {http://geodesic.mathdoc.fr/item/MZ_1971__119_171500/}
}