Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The complexity of the envelope of line and plane arrangements   A facet of an hyperplane arrangement is called external if it belongs to
exactly one bounded cell. The set of all external facets forms the envelope of
the arrangement. The number of external facets of a simple arrangement defined
by $n$ hyperplanes in dimension $d$ is hypothesized to be at least $d{n-2
\choose d-1}$. In this note we show that, for simple arrangements of 4 lines or
more, the minimum number of external facets is equal to $2(n-1)$, and for
simple arrangements of 5 planes or more, the minimum number of external facets
is between $\frac{n(n-2)+6}{3}$ and $(n-4)(2n-3)+5$.

25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat