Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Note on Undecidability of Bisimilarity for Second-Order Pushdown
  Processes   Broadbent and G\"oller (FSTTCS 2012) proved the undecidability of
bisimulation equivalence for processes generated by epsilon-free second-order
pushdown automata. We add a few remarks concerning the used proof technique,
called Defender's forcing, and the related undecidability proof for first-order
pushdown automata with epsilon-transitions (Jan\v{c}ar and Srba, JACM 2008).

7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
3
The categories of this paper are: physics