@article{ZNSL_2005_324_a12,
     author = {S. P. Khekalo},
     title = {Temporary deformations of degrees of the wave operator},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {213--228},
     publisher = {mathdoc},
     volume = {324},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2005_324_a12/}
}