Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Placeholder Substructures II: Meta-Fractals, Made of Box-Kites, Fill
  Infinite-Dimensional Skies
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph