Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Twisting type N vacuums with cosmological constant   We provide the first examples of vacuum metrics with cosmological constant
which have a twisting quadruple principal null direction.

28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph