Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New sum rules for an electron in a periodic or nearly periodic potential   I derive new sum rules for the electronic oscillator strengths in a periodic
or nearly periodic potential, which apply within a single energy band and
between any two bands. The physical origin of these sum rules is quite unlike
that of conventional sum rules, and is shown to be associated with a
solid-state counterpart to the principle of spectroscopic stability known in
atomic physics.

17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph