@article{DAN_1957_116_2_a2,
     author = {M. M. Lavrent'ev},
     title = {The maximum principle in the solutions of strongly elliptical second order systems},
     journal = {Doklady Akademii Nauk},
     pages = {175--176},
     publisher = {mathdoc},
     volume = {116},
     number = {2},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_116_2_a2/}
}