Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Krein's trace formula for unitary operators and operator Lipschitz
  functions   The main result of the paper is a description of the class of functions on
the unit circle, for which Krein's trace formula holds for arbitrary pairs of
unitary operators with trace class difference. We prove that this class of
functions coincides with the class of operator Lipschitz functions.

16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an