Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A direct method of solution for the Fokas-Lenells derivative nonlinear
  Schr\"odinger equation: II. Dark soliton solutions
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
6
The categories of this paper are: astro-ph