Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The definition of quasicrystals   It is argued that the definition of quasicrystals should not include the
requirement that they possess an axis of symmetry that is forbidden in periodic
crystals. The term "quasicrystal" should simply be regarded as an abbreviation
for "quasiperiodic crystal," possibly with two provisos, as discussed below.
The argument is supported by theoretical as well as experimental examples of
quasicrystals without any forbidden symmetry.

28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph