Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Symmetries and Riemann Invariants   To establish a relation between two approaches to the construction of Riemann
k-wave solutions of hydrodynamic-type systems, namely the symmetry reduction
method and the generalized method of characteristics.

5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas