Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral flow and bifurcation for a class of strongly indefinite
  elliptic systems   We consider bifurcation of solutions from a given trivial branch for a class
of strongly indefinite elliptic systems via the spectral flow. Our main results
establish bifurcation invariants that can be obtained from the coefficients of
the systems without using explicit solutions of their linearisations at the
given branch. Our constructions are based on a comparison principle for the
spectral flow and a generalisation of a bifurcation theorem due to Szulkin.

11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph