@article{ZNSL_1972_30_a6,
     author = {V. G. Maz'ya and V. P. Havin},
     title = {Approximation in the mean by harmonic functions},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {91--105},
     publisher = {mathdoc},
     volume = {30},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1972_30_a6/}
}