@article{SM_1993_75_1_a5,
     author = {V. A. Vassiliev},
     title = {Geometry of local lacunae of hyperbolic operators with constant coefficients},
     journal = {Sbornik. Mathematics},
     pages = {111--123},
     publisher = {mathdoc},
     volume = {75},
     number = {1},
     year = {1993},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1993_75_1_a5/}
}