Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Tur\'an problems for digraphs avoiding distinct walks of a given length
  with the same endpoints   Let $n \ge 5$ and $k\ge 4$ be positive integers. We determine the maximum
size of digraphs of order n that avoid distinct walks of length k with the same
endpoints. We also characterize the extremal digraphs attaining this maximum
number when $k \ge 5$.

35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph