@article{DAN_1978_243_5_a11,
     author = {Yu. F. Strugov},
     title = {On a differential property of an extremal mapping quasi-conformal in the mean},
     journal = {Doklady Akademii Nauk},
     pages = {1138--1141},
     publisher = {mathdoc},
     volume = {243},
     number = {5},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1978_243_5_a11/}
}