Conformal field theory
The Hilbert space of physical states is a unitary module of the Virasoro algebra corresponding to a fixed value of "c". Stability requires that the energy spectrum of the Hamiltonian be nonnegative. The modules of interest are the highest weight modules of the Virasoro algebra.
Abelian von Neumann algebra
for measurable families of Hilbert spaces {"H"}, {"K"}. If "U" : "H" → "K" is a unitary such that