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@article{DAN_1967_172_6_a10, author = {M. N. Feller}, title = {On the equation $\Delta U[x(t)]+P[x(t)]U[x(t)]=0$ in a function space}, journal = {Doklady Akademii Nauk}, pages = {1282--1285}, publisher = {mathdoc}, volume = {172}, number = {6}, year = {1967}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1967_172_6_a10/} }
M. N. Feller. On the equation $\Delta U[x(t)]+P[x(t)]U[x(t)]=0$ in a function space. Doklady Akademii Nauk, Tome 172 (1967) no. 6, pp. 1282-1285. http://geodesic.mathdoc.fr/item/DAN_1967_172_6_a10/