@article{SM_1987_58_2_a4,
     author = {A. Fraguela Collar},
     title = {On perturbation of a~polyharmonic operator by delta-like potentials},
     journal = {Sbornik. Mathematics},
     pages = {389--396},
     publisher = {mathdoc},
     volume = {58},
     number = {2},
     year = {1987},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1987_58_2_a4/}
}