@article{VMUMM_1999_4_a11,
     author = {M. V. Ershov},
     title = {On the distortion of subsemigroups},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {56--58},
     publisher = {mathdoc},
     number = {4},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1999_4_a11/}
}