Let $ H$ be a Hilbert space and let $ M$ be a densely defined operator $ D(M) \subset H \to H$ . It is closable iff its adjoint $ M^{\star}$ is densely defined, and then its closure $ \overline{M}$ is $ M^{\star \star}$ . Let $ \mathcal{M}$ be the smallest von Neumann algebra thatRead more