Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Tricomi Equation   The Tricomi equation is a second-order partial differential equation of mixed
elliptic-hyperbolic type. It was first analyzed in the work by Francesco
Giacomo Tricomi (1923) on the well-posedness of a boundary value problem. The
Tricomi equation can be transformed into the corresponding elliptic or
hyperbolic Euler-Poisson-Darboux equation, and has a close connection with
transonic flow and isometric embedding. It has different degeneracy from a
closely related equation, the Keldysh equation.

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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: physics