Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Backlund transformations for the Nizhnik-Novikov-Veselov equation   The Backlund transformations for the Nizhnik-Novikov-Veselov equation are
presented. It is shown that these transformations can be iterated and that the
resulting sequence can be described by the Volterra equations. The
relationships between the Nizhnik-Novikov-Veselov equation and the Volterra
hierarchy are discussed.

3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
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The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: math-ph
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The categories of this paper are: cs
4
The categories of this paper are: cond-mat
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: astro-ph