Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Causal and Topological Structure of the $2$-Dimensional Minkowski
  Space   A list of all possible causal relations in the $2$-dimensional Minkowski
space $M$ is exhausted, based on the duality between timelike and spacelike in
this particular case, and thirty topologies are introduced, all of them
encapsulating the causal structure of $M$. Generalisations of these results are
discussed, as well as their significance in a discussion on spacetime
singularities.

13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg