@article{SM_1981_40_1_a1,
     author = {L. I. Kamynin and B. N. Khimchenko},
     title = {On the strong extremum principle for {a~D-}$(\Pi,\Omega)$-elliptically connected operator of second order},
     journal = {Sbornik. Mathematics},
     pages = {21--50},
     publisher = {mathdoc},
     volume = {40},
     number = {1},
     year = {1981},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1981_40_1_a1/}
}