@article{AL_1990_29_4_a3,
     author = {A. N. Zubkov},
     title = {Varieties of pro-$p$-groups of second-order matrices},
     journal = {Algebra i logika},
     pages = {430--451},
     publisher = {mathdoc},
     volume = {29},
     number = {4},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1990_29_4_a3/}
}