Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chip-Firing and Rotor-Routing on Directed Graphs   We give a rigorous and self-contained survey of the abelian sandpile model
and rotor-router model on finite directed graphs, highlighting the connections
between them. We present several intriguing open problems.

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The categories of this paper are: cond-mat
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The categories of this paper are: eess
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: astro-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: physics
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The categories of this paper are: nucl-th
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The categories of this paper are: econ
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The categories of this paper are: quant-ph