@article{MZM_1999_65_6_a10,
     author = {S. A. Shapovalov},
     title = {The depth invariant for group actions on countable phase spaces},
     journal = {Matemati\v{c}eskie zametki},
     pages = {893--907},
     publisher = {mathdoc},
     volume = {65},
     number = {6},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1999_65_6_a10/}
}