@article{SM_2000_191_7_a1,
     author = {N. I. Dubrovin},
     title = {Formal sums and power series over a~group},
     journal = {Sbornik. Mathematics},
     pages = {955--971},
     publisher = {mathdoc},
     volume = {191},
     number = {7},
     year = {2000},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2000_191_7_a1/}
}