Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological pullback, covering spaces, and a triad of Quillen   We study pullback from a topological viewpoint with emphasis on pullback of
covering maps. We generalize a triad of Quillen on properties of the pullback
functor.

5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci