Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Birational automorphisms of a three-dimensional double quadric with an
  elementary singularity   It is proved that the group of birational automorphisms of a
three-dimensional double quadric with a singular point arising from a double
point on the branch divisor is a semidirect product of the free group generated
by birational involutions of a special form and the group of regular
automorphisms. The proof is based on the method of `untwisting' maximal
singularities of linear systems.

5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn