@article{MAT_1966_10_4_a1,
     author = {I. Berstein},
     title = {On co-groups in the category of graded algebras},
     journal = {Matematika},
     pages = {32--44},
     year = {1966},
     volume = {10},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1966_10_4_a1/}
}