Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A comparison of approximate gravitational lens equations and a proposal
  for an improved new one   Keeping the exact general relativistic treatment of light bending as a
reference, we compare the accuracy of commonly used approximate lens equations.
We conclude that the best approximate lens equation is the Ohanian lens
equation, for which we present a new expression in terms of distances between
observer, lens and source planes. We also examine a realistic gravitational
lensing case, showing that the precision of the Ohanian lens equation might be
required for a reliable treatment of gravitational lensing and a correct
extraction of the full information about gravitational physics.

7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg