@article{MZM_1992_51_4_a10,
     author = {I. V. Mustyatsa},
     title = {Union of derivative chains of two quadratic pencils of unbounded operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {85--90},
     publisher = {mathdoc},
     volume = {51},
     number = {4},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1992_51_4_a10/}
}