[Math] Two reference requests: Pinsker’s inequality and Pontryagin duality

harmonic-analysisit.information-theorypontrjagin-dualityreference-requestsoft-question

Sorry for such a newbie post and for asking two unrelated references in one shot.

First, I am interested in any proof of Pinsker's inequality.

Second, I wonder what is the best place to read about Pontryagin duality and harmonic analysis. To clarify, I took only standard functional analysis course.

Best Answer

Pinsker's inequality has many proofs. My favorites include Pollard's short but "magical" proof, https://www.cs.bgu.ac.il/~asml162/wiki.files/pollard-pinsker.pdf and surely the Proof from the Book is via Hoeffding's inequality+Fenchel-Lagrange duality, as in Theorem 2.16 Massart's book: http://www.cmap.polytechnique.fr/~merlet/articles/probas_massart_stf03.pdf