commutant

The basic mathematical entity to be used here in elucidating the different senses of superselection rules is a von Neumann algebra {{M, a concrete C * -algebra 6 of bounded linear operators acting on a Hilbert space 7 ℋ that is closed in the weak topology 8 or, equivalently, 9 that has the property that (𝔐^′)^′:=𝔐=𝔐, where “′” denotes the commutant.}}