@article{GDZPPN002310007, title = {On the Approximation Numbers of an Operator and Its Adjoint.}, journal = {Mathematische Annalen}, volume = {212}, year = {1974}, pages = {277-280}, zbl = {0272.47017}, url = {http://dml.mathdoc.fr/item/GDZPPN002310007} }
Hutton, C.V. On the Approximation Numbers of an Operator and Its Adjoint.. Mathematische Annalen, Tome 212 (1974) pp. 277-280. http://gdmltest.u-ga.fr/item/GDZPPN002310007/