@article{PismaZhETF.1.15,
    title = {Casimir operators for the unitary group},
    author = {Perelomov, A. M. and Popov, V. M.},
    journal = {Письма в ЖЭТФ},
    volume = {1},
    issue = {6},
    pages = {15},
    year = {1965},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_24436.shtml},
}