@article{PismaZhETF.12.416,
    title = {Mass Operator and Exact Green's Function of an Electron in an Intense Field},
    author = {Ritus, V. I.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {12},
    issue = {8},
    pages = {416},
    year = {1970},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_26344.shtml},
}