@article{SEMR_2005_2_a0,
     author = {J. S. Averina and E. V. Frenkel},
     title = {On strictly sparse subsets of a~free group},
     journal = {Sibirskie \`elektronnye matemati\v{c}eskie izvesti\^a},
     pages = {1--13},
     publisher = {mathdoc},
     volume = {2},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SEMR_2005_2_a0/}
}