Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evolutionary Hirota Type (2+1)-Dimensional Equations: Lax Pairs,
  Recursion Operators and Bi-Hamiltonian Structures   We show that evolutionary Hirota type Euler-Lagrange equations in (2+1)
dimensions have a symplectic Monge-Amp\`ere form. We consider integrable
equations of this type in the sense that they admit infinitely many
hydrodynamic reductions and determine Lax pairs for them. For two
seven-parameter families of integrable equations converted to two-component
form we have constructed Lagrangians, recursion operators and bi-Hamiltonian
representations. We have also presented a six-parameter family of
tri-Hamiltonian systems.

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The categories of this paper are: astro-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: cmp-lg