https://pldml.icm.edu.pl/pldml/element/bwmeta1.element.bwnjournal-article-smv38i1p23bwm
A linear topological characterization of inner-product spaces - Studia Mathematica - Tom 38, Numer...
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https://www.impan.pl/en/publishing-house/journals-and-series/colloquium-mathematicum/all/en/publishing-house/journals-and-series/colloquium-mathematicum/all/24/2/98548/on-semi-inner-product-spaces-i
On semi-inner product spaces, IAll
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