Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Public transport systems in Poland: from Bialystok to Zielona Gora by
  bus and tram using universal statistics of complex networks   We have examined a topology of 21 public transport networks in Poland. Our
data exhibit several universal features in considered systems when they are
analyzed from the point of view of evolving networks. Depending on the assumed
definition of a network topology the degree distribution can follow a power law
p(k) ~ k^(-\gamma) or can be described by an exponential function p(k)
\~exp(-\alpha k). In the first case one observes that mean distances between
two nodes are a linear function of logarithms of their degrees product.

8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat