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All Journal Electronic Journal of Graph Theory and Applications (EJGTA)
Chih, Tien
Oxford College of Emory University
Electrical & Electronics Engineering

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Homotopy covers of graphs Chih, Tien; Scull, Laura
Electronic Journal of Graph Theory and Applications (EJGTA) Vol 14, No 1 (2026): Electronic Journal of Graph Theory and Applications
Publisher : GTA Research Group, Univ. Newcastle, Indonesian Combinatorics Society and ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/ejgta.2026.14.1.1

Abstract

We develop a theory of ×-homotopy, fundamental groupoids and covering spaces that applies to non-simple graphs, generalizing existing results for simple graphs. We prove that ×-homotopies from finite graphs can be decomposed into moves that adjust at most one vertex at a time, generalizing the spider lemma of Chih & Scull (2021). We define a notion of homotopy covering map and develop a theory of universal covers and deck transformations, generalizing Matsushita (2017) and Tardif–Wroncha (2019) to non-simple graphs. We examine the case of reflexive graphs (each vertex having at least one loop). We also prove that these homotopy covering maps satisfy a homotopy lifting property for arbitrary graph homomorphisms, generalizing path lifting results of Matsushita and Tardif–Wroncha.
Co-Authors Scull, Laura