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Let $mathcal{H}$ be a complex separable Hilbert space. We prove that if ${f_{n}}_{n=1}^{infty}$ is a Schauder basis of the Hilbert space $mathcal{H}$, then the angles between any two vectors in this basis must have a positive lower bound. Furthermore, we investigate that ${z^{sigma^{-1}(n)}}_{n=1}^{infty}$ can never be a Schauder basis of $L^{2}(mathbb{T}, u)$, where $mathbb{T}$ is the unit circle, $ u$ is a finite positive discrete measure, and $sigma: mathbb{Z} rightarrow mathbb{N}$ is an arbitrary surjective and injective map.
We extend a theorem of Kato on similarity for sequences of projections in Hilbert spaces to the case of isomorphic Schauder decompositions in certain Banach spaces. To this end we use $ell_{Psi}$-Hilbertian and $infty$-Hilbertian Schauder decompositi
Paley-Wiener theorem for frames for Hilbert spaces, Banach frames, Schauder frames and atomic decompositions for Banach spaces are known. In this paper, we derive Paley-Wiener theorem for p-approximate Schauder frames for separable Banach spaces. We
We present necessary and sufficient conditions to hold true a Kramer type sampling theorem over semi-inner product reproducing kernel Banach spaces. Under some sampling-type hypotheses over a sequence of functions on these Banach spaces it results ne
Famous Naimark-Han-Larson dilation theorem for frames in Hilbert spaces states that every frame for a separable Hilbert space $mathcal{H}$ is image of a Riesz basis under an orthogonal projection from a separable Hilbert space $mathcal{H}_1$ which co
We prove two new equivalences of the Feichtinger conjecture that involve reproducing kernel Hilbert spaces. We prove that if for every Hilbert space, contractively contained in the Hardy space, each Bessel sequence of normalized kernel functions can