@article{DE_1979_15_7_a14,
     author = {L. I. Kamynin and B. N. Khimchenko},
     title = {An isotropic strict extremum principle in a planar domain},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1296--1306},
     publisher = {mathdoc},
     volume = {15},
     number = {7},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1979_15_7_a14/}
}