### Abstract

Under what conditions is it true that if there is a graph homomorphism G H → G T, then there is a graph homomorphism H → T? Let G be a connected graph of odd girth 2k + 1. We say that G is (2 k + 1 )-angulated if every two vertices of G are joined by a path each of whose edges lies on some (2k + 1)-cycle. We call G strongly (2k + 1)-angulated if every two vertices are connected by a sequence of (2k + 1)-cycles with consecutive cycles sharing at least one edge. We prove that if G is strongly (2k + 1)-angulated, H is any graph, S, T are graphs with odd girth at least 2k+ 1, and φ: G H → S T is a graph homomorphism, then either φ maps G {h} to S {t_{h}} for all h ∈ V(H) where t_{h} ∈ V(T) depends on h; or φ maps G {h} to {s_{h}} T for all h ∈ V(H) where s_{h} ∈ V(S) depends on h. This theorem allows us to prove several sufficient conditions for a cancelation law of a graph homomorphism between two box products with a common factor. We conclude the article with some open questions.

Original language | English (US) |
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Pages (from-to) | 221-238 |

Number of pages | 18 |

Journal | Journal of Graph Theory |

Volume | 58 |

Issue number | 3 |

DOIs | |

State | Published - Jul 2008 |

### All Science Journal Classification (ASJC) codes

- Geometry and Topology

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## Cite this

*Journal of Graph Theory*,

*58*(3), 221-238. https://doi.org/10.1002/jgt.20307