Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A proof of Khavinson's conjecture in $\mathbf{R}^4$   The paper deals with an extremal problem for bounded harmonic functions in
the unit ball of $\mathbf{R}^4$. We solve the generalized Khavinson problem in
$\mathbf{R}^4$. This precise problem was formulated by G. Kresin and V. Maz'ya
for harmonic functions in the unit ball and in the half--space of
$\mathbf{R}^n$. We find the optimal pointwise estimates for the norm of the
gradient of bounded real--valued harmonic functions.

10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol