@article{SM_1986_54_1_a9,
     author = {R. I. Grigorchuk},
     title = {On the growth degrees of $p$-groups and torsion-free groups},
     journal = {Sbornik. Mathematics},
     pages = {185--205},
     publisher = {mathdoc},
     volume = {54},
     number = {1},
     year = {1986},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1986_54_1_a9/}
}