@article{CHEB_2017_18_1_a6,
     author = {D. Z. Kagan},
     title = {Invariant functions on free groups and special {HNN-extensions}},
     journal = {\v{C}eby\v{s}evskij sbornik},
     pages = {109--122},
     publisher = {mathdoc},
     volume = {18},
     number = {1},
     year = {2017},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/CHEB_2017_18_1_a6/}
}