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@article{DE_1969_5_12_a15, author = {I. V. Gel'man}, title = {A certain characteristic of normally solvable extensions of a minimal operator}, journal = {Differencialʹnye uravneni\^a}, pages = {2274--2275}, publisher = {mathdoc}, volume = {5}, number = {12}, year = {1969}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1969_5_12_a15/} }
I. V. Gel'man. A certain characteristic of normally solvable extensions of a minimal operator. Differencialʹnye uravneniâ, Tome 5 (1969) no. 12, pp. 2274-2275. http://geodesic.mathdoc.fr/item/DE_1969_5_12_a15/