D. Cariello | Searcharxiv

arXiv2012

On very non-linear subsets of continuous functions

In this paper we continue the study initiated by Gurariy and Quarta in 2004 on the existence of linear spaces formed, up to the null vector, by continuous functions that attain the maximum only at one point. Inserting a topological flavor to the subject, we prove that results already known for functions defined on certain subsets of R are actually true for functions on quite general topological spaces. In the line of the original results of Gurariy and Quarta, we prove that, depending on the desired dimension, such subspaces may exist or not.

math.FA↗

arXiv2012

Subspaces of maximal dimension contained in $L_p(Ω) - \bigcup\limits_{q<p} L_q (Ω)$

Let $(Ω,Σ,μ)$ be a measure space and $1< p < +\infty$. In this paper we show that, under quite general conditions, the set $L_{p}(Ω) - \bigcup\limits_{1 \leq q < p}L_{q}(Ω)$ is maximal spaceable, that is, it contains (except for the null vector) a closed subspace $F$ of $L_{p}(Ω)$ such that $\dim(F) = \dim(L_{p}(Ω))$. We also show that if those conditions are not fulfilled, then even the larger set $L_p(Ω) - L_q(Ω)$, $1 \leq q < p$, may fail to be maximal spaceable. The aim of the results presented here is, among others, to generalize all the previous work (since the 1960's) related to the linear structure of the sets $L_{p}(Ω) - L_{q}(Ω)$ with $q < p$ and $L_{p}(Ω) - \bigcup\limits_{1 \leq q < p}L_{q}(Ω)$.

math.FA↗