Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the classification of left-invariant para-K\"{a}hler structures on
  four-dimensional Lie groups   A first classification of para-K\"{a}hler structures on four-dimensional Lie
algebras was obtained by D. Calvaruzo in 2015. In this paper, we propose
another classification based on the classification of symplectic Lie algebras.
For each four-dimensional symplectic Lie algebra, compatible para-complex
structures and the corresponding pseudo-Riemannian metrics are found in
explicit form. This leads to the classification of Sasaki para-contact
structures on five-dimensional contact Lie algebras with a nontrivial center.

0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int