Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Visibility of Gravitational Lenses and the Cosmological Constant Problem   Recent observations suggest appreciable star formation activity in early-type
galaxies down to redshift $z\sim 0.5$. If so, there is likely to be dust in
these galaxies. We consider the possibility that obscuration by dust can
reconcile the observed frequency of gravitational lensing of quasar images with
the considerably larger rate predicted in a low density cosmologically flat
universe dominated by a cosmological constant.

12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn