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Second question on a real sequence
I am thinking again about the real sequence $\{a_n\}_{n\ge1}$ which decays faster than any algebraic speed, that is, $\lim_{n\to \infty}n^pa_n = 0$ for every integer $p$. Actually, $a_n$ can be ...
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$\|f\|^2_{H^{-1}(\mathbb{T})}\lesssim \int_\mathbb{T} |\sin(x)f(x)|^2 \; dx$?
I have been stuck in this question for a while, and I would appreciate any new ideas. I have been considering the inequality
$$
\|f\|^2_{H^{-1}(\mathbb{T})}\lesssim \int_\mathbb{T} |\sin(x)f(x)|^2 \; ...