@article{RM_1978_33_2_a9,
     author = {E. I. Glazman},
     title = {Extensions of differential-difference operators with periodic
},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {229--230},
     publisher = {mathdoc},
     volume = {33},
     number = {2},
     year = {1978},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1978_33_2_a9/}
}