@article{SM_1970_11_2_a3,
     author = {E. G. Sitnikova},
     title = {A~three spheres theorem for an elliptic equation of high order},
     journal = {Sbornik. Mathematics},
     pages = {189--195},
     publisher = {mathdoc},
     volume = {11},
     number = {2},
     year = {1970},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1970_11_2_a3/}
}