Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extended Geometry of Black Holes   We reconsider space-time singularities in classical Einsteinian general
relativity: with the help of several new co-ordinate systems we show that the
Schwarzschild solution can be extended beyond the curvature singularity at r=0.
The extension appears as an infinite covering of standard Kruskal space-time.
While the two-dimensional reduction of this infinite sequence of
Kruskal-Szekeres domains obtained by suppressing the angular degrees of freedom
is still a topological manifold - albeit one for which the metric structure is
singular on one-dimensional submanifolds - we obtain for the full
four-dimensional geometry the more general structure of a stratified variety.

2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin