Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Three Key Tests to Gravity   Three presumably unrelated open questions concerning gravity and the
structure of the Universe are here discussed: 1) To which extent is Lorentz
invariance an exact symmetry ? 2) What is the equation of state of the Universe
? 3) What is the origin of the so-called Pioneer anomaly ?

13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
2
The categories of this paper are: math