@article{BUMI_1967_3_22_4_a8,
     author = {Rus, Ioan A.},
     title = {Th\'eor\`emes de comparaison pour les syst\`emes elliptiques aux  d\'eriv\'ees partielles du second ordre.},
     journal = {Bollettino della Unione matematica italiana},
     pages = {486--490},
     publisher = {mathdoc},
     volume = {Ser. 3, 22},
     number = {4},
     year = {1967},
     zbl = {0153.14801},
     mrnumber = {226182},
     url = {http://geodesic.mathdoc.fr/item/BUMI_1967_3_22_4_a8/}
}