Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Direct observation of the oxygen isotope effect on the in-plane magnetic
  field penetration depth in optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn