Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-orientable Lagrangian surfaces in rational 4-manifolds   We show that for any nonzero class $A$ in $H_2(X; \mathbb{Z}_2)$ in a
rational 4-manifold $X$, $A$ is represented by a nonorientable embedded
Lagrangian surface L (for some symplectic structure) if and only if $P(A)\equiv
(L) (mod\ 4)$; where $P(A)$ denotes the mod 4 valued Pontrjagin square of $A$.

11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
3
The categories of this paper are: physics
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph