@article{AL_2007_46_3_a1,
     author = {A. A. Klyachko},
     title = {Free subgroups of one-relator relative presentations},
     journal = {Algebra i logika},
     pages = {290--298},
     publisher = {mathdoc},
     volume = {46},
     number = {3},
     year = {2007},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2007_46_3_a1/}
}