@article{JETPL.98.549,
    title = {},
    author = {Volovik, G. E.},
    journal = {JETP Lett.},
    volume = {98},
    issue = {8},
    pages = {491},
    year = {2013},
    doi = {},
    url = {http://jetpletters.ru/ps/dx/10.7868/S0370274X13200113},
    note = {[Pisma v ZhETF 98, 549 (2013)]}
}