@article{SM_1979_35_4_a3,
     author = {V. P. Polityukov},
     title = {On the theory of upper and lower solutions and the solvability of quasilinear integro-differential equations},
     journal = {Sbornik. Mathematics},
     pages = {499--507},
     year = {1979},
     volume = {35},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1979_35_4_a3/}
}