@article{PismaZhETF.97.344,
    title = {Nambu sum rule in the NJL models: from superfluidity to top quark condensation},
    author = {Volovik, G. E. and Zubkov, M. A.},
    journal = {Письма в ЖЭТФ},
    volume = {97},
    issue = {6},
    pages = {344},
    year = {2013},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_30232.shtml},
    note = {[JETP Letters 97, 301 (2013)]}
}