@article{MABA_1997_11_1-2_a6,
     author = {Raina Ivanova},
     title = {An {Orthogonal} {Tangential} {Group} of {Transformations} of a {4-Dimensional} {Riemannian} {Manifold}},
     journal = {Mathematica balkanica},
     pages = {57},
     publisher = {mathdoc},
     volume = {11},
     number = {1-2},
     year = {1997},
     url = {http://geodesic.mathdoc.fr/item/MABA_1997_11_1-2_a6/}
}