Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: QED and Fundamental Symmetries in Positronium Decays   We discuss positronium decays with emphasis on tests of fundamental
symmetries and the constraints from measurements of other precision observables
involving electrons and photons.

20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph