@article{SM_1971_13_3_a2,
     author = {R. Denchev},
     title = {On commuting selfadjoint extensions of differential operators},
     journal = {Sbornik. Mathematics},
     pages = {360--369},
     publisher = {mathdoc},
     volume = {13},
     number = {3},
     year = {1971},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1971_13_3_a2/}
}