Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On Ascent, Repetition and Descent Sequences   Ascent sequences have received a lot of attention in recent years in
connection with (2 + 2)-free posets and other combinatorial objects. Here, we
first show bijectively that analogous repetition sequences are counted by the
Bell numbers, and 021-avoiding repetition sequences by the Catalan numbers.
Then we adapt a bijection of Chen et al and use it along with the "symbolic"
method of Flajolet to find the 4-variable generating function for 021-avoiding
ascent sequences by length, number of 0's, number of isolated 0's, and number
of runs of 2 or more 0's. We deduce that 021-avoiding ascent sequences that
have no consecutive 0's (resp. no isolated 0's) both satisfy a Catalan-like
recurrence, differing only in initial conditions, and give a bijective proof
for the case of no consecutive 0's. Lastly, we show that 021-avoiding descent
sequences are equinumerous with same-size $UUDU$-avoiding Dyck paths.

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The categories of this paper are: q-bio
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The categories of this paper are: supr-con
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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The categories of this paper are: adap-org
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The categories of this paper are: physics
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The categories of this paper are: eess
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol