Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the complexity of identifying Head Elementary Set Free programs   Head-elementary-set-free programs were proposed in (Gebser et al. 2007) and
shown to generalize over head-cycle-free programs while retaining their nice
properties. It was left as an open problem in (Gebser et al. 2007) to establish
the complexity of identifying head-elementary-set-free programs. This note
solves the open problem, by showing that the problem is complete for co-NP.

12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol