Submission date: 5 December 2018

Abstract:

In this paper, we state and prove two Fraïssé-style results that cover existence and uniqueness properties for twelve of the eighteen different notions of homomorphism-homogeneity as introduced by Lockett and Truss, and provide forward directions and implications for the remaining six cases. Following these results, we completely determine the extent to which the countable homogeneous undirected graphs (as classified by Lachlan and Woodrow) are homomorphism-homogeneous; we also provide some insight into the directed graph case.

Mathematics Subject Classification: 03C15, 05C63

Keywords and phrases:

Full text arXiv 1812.01934: pdf, ps.