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@article{MZ_1953__59_169376, author = {David Ellis}, title = {A {Modification} of the {Parallelogram} {Law} {Characterization} of {Hilbert} {Spaces.}}, journal = {Mathematische Zeitschrift}, pages = {94--96}, publisher = {mathdoc}, volume = {59}, year = {1953}, zbl = {0051.08601}, url = {http://geodesic.mathdoc.fr/item/MZ_1953__59_169376/} }
David Ellis. A Modification of the Parallelogram Law Characterization of Hilbert Spaces.. Mathematische Zeitschrift, Tome 59 (1953), pp. 94-96. http://geodesic.mathdoc.fr/item/MZ_1953__59_169376/