Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A gentle introduction to Schwinger's formulation of quantum mechanics:
  The groupoid picture   In this short letter we review Schwinger's formulation of Quantum Mechanics
and we argue that the mathematical structure behind Schwinger's "Symbolism of
Atomic Measurements" is that of a groupoid. In this framework, both the Hilbert
space (Schr\"{o}dinger picture) and the $C^{*}$-algebra (Heisenberg picture) of
the system turn out to be derived concepts, that is, they arise from the
underlying groupoid structure.

26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph