A Homology Theory of Graphs: First Homology Group of Hamiltonian Graphs

Abstract

An integral homology theory on the category of undirected reflexive graphs was constructed in [2]. A geometrical method to understand behaviors of $1$- and $2$-simplices under differential maps of the theory was developed in [3] and led us to an independent proof that the first homology group of any cycle graphs is $\mathbb{Z}$, as it was proved before by a version of Hurewicz theorem harshly defined and shown in [1] and [2]. In this work, we use the old method in [3] to study behaviors of the first homology group of Hamiltonian graphs. We discovered that $H_1(G)$ is torsion-free, for any Hamiltonian graphs $G$.