Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Schwinger's picture of Quantum Mechanics   In this paper we will present tha main features of what can be called
Schwinger's foundational approach to Quantum Mechanics. The basic ingredients
of this formulation are the \textit{selective measurements}, whose algebraic
composition rules define a mathematical structure called groupoid, which is
associated with any physical system. After the introduction of the basic axioms
of a groupoid, the concepts of observables and states, statistical
interpretation and evolution are derived. An example is finally introduced to
support the theoretical description of this approach.

23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga