Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An omega-power of a context-free language which is Borel above
  Delta^0_omega   We use erasers-like basic operations on words to construct a set that is both
Borel and above Delta^0_omega, built as a set V^\omega where V is a language of
finite words accepted by a pushdown automaton. In particular, this gives a
first example of an omega-power of a context free language which is a Borel set
of infinite rank.

12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat