@article{MET_1988__35_3-4_176152,
     author = {R. Gr\"ubel},
     title = {A {Minimal} {Characterization} of the {Covariance} {Matrix.}},
     journal = {Metrika},
     pages = {49--52},
     publisher = {mathdoc},
     volume = {35},
     number = {3-4},
     year = {1988},
     zbl = {0638.62046},
     url = {http://geodesic.mathdoc.fr/item/MET_1988__35_3-4_176152/}
}