Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classification of evolutionary equations on the lattice. I. The general
  theory   A modification of the symmetry approach for the classification of integrable
differential-difference equations of the form $$ u_{n,t} = f_n(u_{n-1}, u_n,
u_{n+1}), $$ where $n$ is a discrete integer variable, is presented (the
well-known Volterra and Toda equations can be written in this form). If before,
in the framework of the symmetry approach, only equations similar to $$ u_{n,t}
= f(u_{n-1}, u_n, u_{n+1}), $$ i.e. defined by a function $f$, were considered,
now we have an infinite set $f_n$ of a priori quite different functions.

27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
6
The categories of this paper are: astro-ph