@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/}
}