On well quasi-order of graph classes under homomorphic image orderings
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In this paper we consider the question of well quasi-order for classes defined by a single obstruction within the classes of all graphs, digraphs and tournaments, under the homomorphic image ordering (in both its standard and strong forms). The homomorphic image ordering was introduced by the authors in a previous paper and corresponds to the existence of a surjective homomorphism between two structures. We obtain complete characterisations in all cases except for graphs under the strong ordering, where some open questions remain.
Huczynska , S & Ruškuc , N 2017 , ' On well quasi-order of graph classes under homomorphic image orderings ' European Journal of Combinatorics , vol 63 , pp. 164-175 . DOI: 10.1016/j.ejc.2017.03.008
European Journal of Combinatorics
© 2017 Elsevier Ltd. All rights reserved. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.ejc.2017.03.008
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