Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chronology Protection in Two-Dimensional Dilaton Gravity   The global structure of 1 + 1 dimensional compact Universe is studied in
two-dimensional model of dilaton gravity.
  First we give a classical solution corresponding to the spacetime in which a
closed time-like curve appears, and show the instability of this spacetime due
to the existence of matters.
  We also observe quantum version of such a spacetime having closed timelike
curves never reappear unless the parameters are fine-tuned.

25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat
6
The categories of this paper are: astro-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg