@article{MZM_1991_50_6_a0,
     author = {A. M. Akimenkov},
     title = {Subgroups of the braid group $B_4$},
     journal = {Matemati\v{c}eskie zametki},
     pages = {3--13},
     year = {1991},
     volume = {50},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1991_50_6_a0/}
}