@article{EJDE_2006__2006__a116,
     author = {Kryzhevich, Sergey G. and Volpert, Vitaly A.},
     title = {Different types of solvability conditions for differential operators},
     journal = {Electronic Journal of Differential Equations},
     publisher = {mathdoc},
     volume = {2006},
     year = {2006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2006__2006__a116/}
}