@article{GDZPPN00238387X,
title = {A Modification of the Parallelogram Law Characterization of Hilbert Spaces.},
journal = {Mathematische Zeitschrift},
volume = {59},
year = {1953},
pages = {94-96},
zbl = {0051.08601},
url = {http://dml.mathdoc.fr/item/GDZPPN00238387X}
}
Ellis, David. A Modification of the Parallelogram Law Characterization of Hilbert Spaces.. Mathematische Zeitschrift, Tome 59 (1953) pp. 94-96. http://gdmltest.u-ga.fr/item/GDZPPN00238387X/