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@article{PORMA_1967__26_3_115039, author = {Gilbert, R.P. and Howard, H.C.}, title = {On a class of elliptic partial differential equations}, journal = {Portugaliae mathematica}, pages = {353--373}, publisher = {mathdoc}, volume = {26}, number = {3}, year = {1967}, zbl = {0195.11201}, language = {en}, url = {http://geodesic.mathdoc.fr/item/PORMA_1967__26_3_115039/} }
Gilbert, R.P.; Howard, H.C. On a class of elliptic partial differential equations. Portugaliae mathematica, Tome 26 (1967) no. 3, pp. 353-373. http://geodesic.mathdoc.fr/item/PORMA_1967__26_3_115039/