@article{PismaZhETF.57.796,
    title = {Variational bound for the energy of two-dimensional quantum antiferromagnet},
    author = {Ovchinnikov, A. A.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {57},
    issue = {12},
    pages = {796},
    year = {1993},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_4957.shtml},
}