Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The regularity of sonic curves for the two-dimensional Riemann problems
  of the nonlinear wave system of Chaplygin gas   We study the regularity of sonic curves to a two-dimensional Riemann problem
for the nonlinear wave system of Chaplygin gas, which is an essential step for
the global existence of solutions to the two-dimensional Riemann problems. As a
result, we establish the global existence of uniformly smooth solutions in the
semi-hyperbolic patches up to the sonic boundary, where the degeneracy of
hyperbolicity occurs. Furthermore, we show the C^1 regularity of sonic curves.

31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
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The categories of this paper are: q-alg
16
The categories of this paper are: stat
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph