@article{PismaZhETF.6.772,
    title = {Physical Limitations on the Topology of the Universe},
    author = {Zel'dovich, Ya. B. and Novikov, I. D.},
    journal = {Письма в ЖЭТФ},
    volume = {6},
    issue = {7},
    pages = {772},
    year = {1967},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_25485.shtml},
}