English

Rigidity of sets of independent functions in symmetric spaces

Functional Analysis 2026-07-07 v1

Abstract

We say that a symmetric function space XX has the (IR)(IR) property whenever all sets of NN independent mean zero functions f1,,fNXf_1,\ldots,f_N\in X, fkX1\|f_k\|_X\ge 1, are poorly approximated by any linear combinations of arbitrary nn functions, if nn is sufficienly smaller that NN; namely, for some γ=γ(X)>0\gamma=\gamma(X)>0 we have dn({f1,,fN},X)γd_n(\{f_1,\ldots,f_N\},X)\ge \gamma, nγNn\le \gamma N, where dn(K,X)d_n(K,X) is the Kolmogorov nn-width of the set KXK\subset X. The spaces X=LpX=L_p satisfy this property if and only if 1p21\le p\le2 or p=p=\infty. The goal of this paper is to move from LpL_p scale to a larger class of symmetric spaces. We obtain rather broad conditions, under which such a space XX has the (IR)(IR) property and prove precise statements for particular scales of Lorentz Lp,qL_{p,q} spaces and Orlicz spaces.

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Cite

@article{arxiv.2607.06530,
  title  = {Rigidity of sets of independent functions in symmetric spaces},
  author = {Sergey V. Astashkin and Yu. V. Malykhin},
  journal= {arXiv preprint arXiv:2607.06530},
  year   = {2026}
}

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24 pages