Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Combinatorial reciprocity for the chromatic polynomial and the chromatic
  symmetric function   Let G be a graph, and let $\chi$G be its chromatic polynomial. For any
non-negative integers i, j, we give an interpretation for the evaluation $\chi$
(i) G (--j) in terms of acyclic orientations. This recovers the classical
interpretations due to Stanley and to Green and Zaslavsky respectively in the
cases i = 0 and j = 0. We also give symmetric function refinements of our
interpretations, and some extensions. The proofs use heap theory in the spirit
of a 1999 paper of Gessel.

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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: cond-mat
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: plasm-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin