Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Emergence of massless Dirac fermions in graphene's Hofstadter butterfly
  at switches of the quantum Hall phase connectivity
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg