@article{GDZPPN001165615, title = {An Elementary Proof of the Hopf Inequality for Positive Operators.}, journal = {Numerische Mathematik}, volume = {7}, year = {1965}, pages = {331-337}, zbl = {0148.38103}, url = {http://dml.mathdoc.fr/item/GDZPPN001165615} }
BAUER, F.L. An Elementary Proof of the Hopf Inequality for Positive Operators.. Numerische Mathematik, Tome 7 (1965) pp. 331-337. http://gdmltest.u-ga.fr/item/GDZPPN001165615/