@article{PismaZhETF.43.453,
    title = {Possible number of different neutrinos},
    author = {Man'ko, V. I. and Markov, M. A.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {43},
    issue = {10},
    pages = {453},
    year = {1986},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_21383.shtml},
}