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@article{IVM_1977_8_a15, author = {A. B. Livchak}, title = {Formula subsets of the ordered group of integers}, journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika}, pages = {105--107}, publisher = {mathdoc}, number = {8}, year = {1977}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/IVM_1977_8_a15/} }
A. B. Livchak. Formula subsets of the ordered group of integers. Izvestiâ vysših učebnyh zavedenij. Matematika, no. 8 (1977), pp. 105-107. http://geodesic.mathdoc.fr/item/IVM_1977_8_a15/