@article{EJDE_2001__2001__a168,
     author = {El Haial, Abdelillah and Labbas, Rabah},
     title = {On the ellipticity and solvability of an abstract second-order differential equation},
     journal = {Electronic Journal of Differential Equations},
     publisher = {mathdoc},
     volume = {2001},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2001__2001__a168/}
}