@article{FAA_2011_45_4_a0,
     author = {A. A. Agrachev},
     title = {On the space of symmetric operators with multiple ground states},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {1--15},
     publisher = {mathdoc},
     volume = {45},
     number = {4},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_2011_45_4_a0/}
}