@article{DE_1980_16_10_a18,
     author = {L. N. Lyapin},
     title = {Upper and lower solution of equations of evolution type},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1885--1887},
     publisher = {mathdoc},
     volume = {16},
     number = {10},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_10_a18/}
}