Positive Positive Definite Discrete Strong Almost Periodic Measures and Bragg Diffraction

In this paper we prove that the cone $\PPD$ of positive, positive definite, discrete and strong almost periodic measures has an interesting property: given any positive and positive definite measure $μ$ smaller than some measure in $\PPD$, then the strong almost periodic part $μ_S$ of $μ$ is also in $\PPD$. We then use this result to prove that given a positive weighted comb $ω$ with finite local complexity and pure point diffraction, any positive comb less than $ω$ has either trivial Bragg spectrum or a relatively dense set of Bragg peaks.

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