English

The Set-Self-Tietze Property

General Topology 2026-03-17 v1

Abstract

We introduce the set-self-Tietze property, an analogue of the self-Tietze property for upper semi-continuous set-valued functions. A topological space XX is self-Tietze, if for every closed AXA \subseteq X and continuous function f ⁣:AXf \colon A \to X, there is a continuous extension F ⁣:XXF \colon X \to X of ff. A topological space XX is set-self-Tietze, if for every closed AXA \subseteq X and upper semi-continuous set-valued function f ⁣:A2Xf \colon A \to 2^X, there exists an upper semi-continuous set-valued function F ⁣:X2XF \colon X \to 2^X such that FA=f\left. F \right|_A = f. We show every compact metric space is set-self-Tietze, and that the torus is not self-Tietze.

Keywords

Cite

@article{arxiv.2603.14404,
  title  = {The Set-Self-Tietze Property},
  author = {Andrew Wood},
  journal= {arXiv preprint arXiv:2603.14404},
  year   = {2026}
}
R2 v1 2026-07-01T11:20:45.324Z