@article{DE_1999_35_6_a11,
     author = {\`E. M. Solnechnyi},
     title = {On the causality of operators that arise in problems of mathematical physics with weak nonlinearities},
     journal = {Differencialʹnye uravneni\^a},
     pages = {801--808},
     publisher = {mathdoc},
     volume = {35},
     number = {6},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_6_a11/}
}