@article{ZNSL_2002_289_a15,
     author = {E. A. Sopkina},
     title = {On the sum of roots of a closed set},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {277--286},
     year = {2002},
     volume = {289},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2002_289_a15/}
}