Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low dimensional Lie groups admitting left invariant flat projective or
  affine structures   We prove that any real Lie group of dimension \leq 5 admits a left invariant
flat projective structure. We also prove that a real Lie group L of dimension
\leq 5 admits a left invariant flat affine structure if and only if the Lie
algebra of L is not perfect.

24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci