Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Almost complex structures that are harmonic maps   We find geometric conditions on a four-dimensional almost Hermitian manifold
under which the almost complex structure is a harmonic map or a minimal
isometric imbedding of the manifold into its twistor space.

14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat