@article{1077492271, author = {Calkin, J. W.}, title = {Symmetric transformations in Hilbert space}, journal = {Duke Math. J.}, volume = {6}, number = {1}, year = {1940}, pages = { 504-508}, language = {en}, url = {http://dml.mathdoc.fr/item/1077492271} }
Calkin, J. W. Symmetric transformations in Hilbert space. Duke Math. J., Tome 6 (1940) no. 1, pp. 504-508. http://gdmltest.u-ga.fr/item/1077492271/