Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classical differential geometry and integrability of systems of
  hydrodynamic type   Remarkable parallelism between the theory of integrable systems of
first-order quasilinear PDE and some old results in projective and affine
differential geometry of conjugate nets, Laplace equations, their
Bianchi-Baecklund transformations is exposed.
  These results were recently applied by I.M.Krichever and B.A.Dubrovin to
prove integrability of some models in topological field theories. Within the
geometric framework we derive some new integrable (in a sense to be discussed)
generalizations describing N-wave resonant interactions.

31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex