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Feb 4, 2020 at 15:52 history edited YCor CC BY-SA 4.0
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Feb 4, 2020 at 15:45 history edited I love pineapple coffee CC BY-SA 4.0
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Feb 2, 2020 at 23:52 comment added YCor Could you be more precise about the space on which you want information about this operator. In particular, are you really interested about your questions in the whole topological vector space $\mathbf{R}^\mathbf{\mathbf{Z}}$?
Feb 2, 2020 at 19:16 comment added Nemo If you are looking for earliest references then see Phillips and Wiener, "Nets and Dirichlet problem" (1923).
Feb 2, 2020 at 19:07 comment added Christian Remling Here I'm of course assuming that you defined the operator on $\ell^2(\mathbb Z)$.
Feb 2, 2020 at 19:06 comment added Christian Remling There won't be any references that discuss this operator at length since it's very easy to analyze: just take Fourier transforms $Fx = \sum x_n e^{int}$ to represent $\Delta$ as multiplication by $2(1-\cos t)$ in $L^2(-\pi,\pi)$. This immediately answers all your questions (for example, the spectrum equals $[0,4]$, is purely ac of multiplicitly $2$).
Feb 2, 2020 at 18:56 history asked I love pineapple coffee CC BY-SA 4.0