Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Towards a theory of thin self-gravitating crossing shells   In the case of crossing thin dust shells the momentum conservation law is
found. For two crossing isotropic shells it coincides with the 't Hooft-Dray
formula. The system of one isotropic and one time-like shell is considered. In
this case we found a very simple formula which relate velocities of dust shell
before and after crossing.

29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph