Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Wohlfahrt's Theorem for the Hecke group G_5   Let K be a subgroup of the inhomogeneous Hecke group G_5 of finite index.
Suppose that the geometric level of K is r. Then K is congruence if and only if
K contains the principal congruence subgroup of level 2r.

31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
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The categories of this paper are: eess
23
The categories of this paper are: solv-int
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph