Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Darboux Covariant Equations of von Neumann Type and their
  Generalizations   Lax pairs with operator valued coefficients, which are explicitly connected
by means of an additional condition, are considered. This condition is proved
to be covariant with respect to the Darboux transformation of a general form.
Nonlinear equations arising from the compatibility condition of the Lax pairs
in the matrix case include, in particular, Nahm equations, Volterra,
Bogoyavlenskii and Toda lattices. The examples of another one-, two- and
multi-field lattice equations are also presented.

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The categories of this paper are: hep-th
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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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: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: acc-phys