Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomaly-free $W$-gravity Theories   We give a review of some recent developments in the quantisation of
$W$-gravity theories. In particular, we discuss the construction of
anomaly-free $W_\infty$ and $W_3$ gravities.

21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph