Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonzero positive solutions of elliptic systems with gradient dependence
  and functional BCs   We discuss, by topological methods, the solvability of systems of
second-order elliptic differential equations subject to functional boundary
conditions under the presence of gradient terms in the nonlinearities. We prove
the existence of non-negative solutions and provide a non-existence result. We
present some examples to illustrate the applicability of the existence and
non-existence results.

30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci