Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On well quasi-order of graph classes under homomorphic image orderings   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 characterizations in all cases
except for graphs under the strong ordering, where some open questions remain.

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The categories of this paper are: solv-int
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The categories of this paper are: stat
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
6
The categories of this paper are: astro-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
1
The categories of this paper are: cs