Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Limit groups as limits of free groups: compactifying the set of free
  groups   We give a topological framework for the study of Sela's limit groups: limit
groups are limits of free groups in a compact space of marked groups. Many
results get a natural interpretation in this setting. The class of limit groups
is known to coincide with the class of finitely generated fully residually free
groups. The topological approach gives some new insight on the relation between
fully residually free groups, the universal theory of free groups,
ultraproducts and non-standard free groups.

26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys