Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic censorship of smooth structures   It is observed that on many 4-manifolds there is a unique smooth structure
underlying a globally hyperbolic Lorentz metric. For instance, every
contractible smooth 4-manifold admitting a globally hyperbolic Lorentz metric
is diffeomorphic to the standard $\R^4$. Similarly, a smooth 4-manifold
homeomorphic to the product of a closed oriented 3-manifold $N$ and $\R$ and
admitting a globally hyperbolic Lorentz metric is in fact diffeomorphic to
$N\times \R$. Thus one may speak of a censorship imposed by the global
hyperbolicty assumption on the possible smooth structures on
$(3+1)$-dimensional spacetimes.

29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
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
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin