TY - JOUR AU - Sokolov, Maksim S. TI - An abstract approach to some spectral problems of direct sum differential operators JO - Electronic Journal of Differential Equations PY - 2003 VL - 2003 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/EJDE_2003__2003__a116/ LA - en ID - EJDE_2003__2003__a116 ER -