Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: FHCP Challenge Set: The First Set of Structurally Difficult Instances of
  the Hamiltonian Cycle Problem
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat