@article{DE_2005_41_8_a7,
     author = {Yu. A. Klokov},
     title = {On {Upper} and {Lower} {Functions} for a {Fourth-Order} {Ordinary} {Differential} {Equation:} {I}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1074--1083},
     publisher = {mathdoc},
     volume = {41},
     number = {8},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2005_41_8_a7/}
}