There is a Banach algebra satisfying the von Neumann inequality for polynomials in a single variable, without constant term, which is not isomorphic to a norm-closed algebra of operators on a Hilbert space.
Keywords:
Mathematics Unital Von Neumann algebra Von Neumann architecture Pure mathematics Abelian von Neumann algebra Norm (philosophy) Hilbert space Affiliated operator Inequality Algebra over a field Jordan algebra Mathematical analysis Algebra representation