@article{SM_1968_6_2_a2,
     author = {G. I. \`Eskin},
     title = {Systems of pseudodifferential equations with simple real characteristics},
     journal = {Sbornik. Mathematics},
     pages = {159--183},
     publisher = {mathdoc},
     volume = {6},
     number = {2},
     year = {1968},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1968_6_2_a2/}
}