Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classes of second order nonlinear differential equations reducible to
  first order ones by variation of parameters   The method of parameter variation for linear differential equations is
extended to classes of second order nonlinear differential equations. This
allows to reduce the latter to first order differential equations. Known
classical equations such as the Bernoulli, Riccati and Abel equations are
recovered in illustrated relevant examples.

21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat