Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Real Algebraic Threefolds IV: Del Pezzo Fibrations   This is the fourth of a series of papers studying real algebraic threefolds,
but the methods are mostly independent from the previous ones. Let $f:X\to C$
be a map of a smooth projective real algebraic 3-fold to a curve $C$ whose
general fibers are rational surfaces.
  Assume that the set of real points of $X$ is an orientable 3-manifold $M$.
The aim of the paper is to give a topological description of $M$.

23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
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
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph