Lineability of functions in $C(K)$ with specified range

Abstract

This paper is inspired by the paper of Leonetti, Russo and Somaglia [\textit{Dense lineability and spaceability in certain subsets of ${\ell }_{\infty }$.} Bull. London Math. Soc., 55: 2283--2303 (2023)] and the lineability problems raised therein. It concerns the properties of ${\ell }_{\infty }$ subsets defined by cluster points of sequences. Using the fact that the set of cluster points of a sequence $x$ depends only on its equivalence class in ${\ell }_{\infty }/c_0$ and that the quotient space ${\ell }_{\infty }/c_0$ is isometrically isomorphic to $C(\beta \mathbb{N}\setminus \mathbb{N})$, we are able to translate lineability problems from ${\ell }_{\infty }$ to $C(\beta \mathbb{N}\setminus \mathbb{N})$. We prove that for a compact space $K$ with properties similar to those of $\beta \mathbb{N}\setminus \mathbb{N}$, the sets of continuous functions $f$ in $C(K)$ with $|\mathrm{rng}(f)|=\omega$ and those $f$ with $|\mathrm{rng}(f)|=\mathfrak{c}$ contain, up to zero function, an isometric copy of $c_0(\kappa )$ for uncountable cardinal $\kappa$. Specializing those results to some closed subspaces $K$ of $\beta \mathbb{N}\setminus \mathbb{N}$ we are able to generalize known results to their ideal versions.