@article{DAN_1957_116_5_a9,
     author = {P. E. Sobolevskii},
     title = {On equations with operators forming an acute angle},
     journal = {Doklady Akademii Nauk},
     pages = {754--757},
     publisher = {mathdoc},
     volume = {116},
     number = {5},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_116_5_a9/}
}