Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Invariance of density correlations with charge density in
  polyelectrolyte solutions
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an