“…The results obtained by this approach are mostly consequences of our results. In particular, Andersson [2003] showed that the functional calculus can be extended via the Cauchy-Green formula to the algebra of C ∞ functions with an additional condition at infinity if and only if the corresponding group is polynomially bounded, although a wider class of operators admits functional calculus for test functions. Andersson, Samuelsson and Sandberg [2006] observed that for any proper f ∈ C ∞ ޒ( m , ޒ k ), the set {g • f | g ∈ Ᏸ(ޒ k )} is contained in D(ޒ m ); they then used this fact to construct the functional calculus (with test functions) for f (A), where f is a proper C ∞ function and A is a Helffer-Sjöstrand operator, that is, an operator with real spectrum and rationally bounded resolvent on compacts.…”