Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Biorthogonal systems on unit interval and zeta dilation operators   An elementary 'quantum-mechanical' derivation of the conditions for a system
of functions to form a Reisz basis of a Hilbert space on a finite interval is
presented.

6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci