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Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

14 votes

When is a Banach space a Hilbert space?

More characterisations are in the book of Haim Brezis (Analyse fonctionnelle), at the appendix of Chapter 5. I will copy two of these below, toghether with the references: If $ \dim(E)\geq 2 $ and e …
Garrisi Daniele's user avatar