Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The number of Z-convex polyominoes   In this paper we consider a restricted class of convex polyominoes that we
call Z-convex polyominoes. Z-convex polyominoes are polyominoes such that any
two pairs of cells can be connected by a monotone path making at most two turns
(like the letter Z). In particular they are convex polyominoes, but they appear
to resist standard decompositions. We propose a construction by ``inflation''
that allows to write a system of functional equations for their generating
functions. The generating function P(t) of Z-convex polyominoes with respect to
the semi-perimeter turns out to be algebraic all the same and surprisingly,
like the generating function of convex polyominoes, it can be expressed as a
rational function of t and the generating function of Catalan numbers.

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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: astro-ph
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The categories of this paper are: cs
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The categories of this paper are: nlin
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The categories of this paper are: plasm-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: eess