Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Simple Path to Biggins' Martingale Convergence for Branching Random
  Walk   We give a simple non-analytic proof of Biggins' theorem on martingale
convergence for branching random walks.

23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs