The exponential calculus of microdifferential operators of infinite order. IV
[For part III see the article reviewed above.] The exponential of a \(micro(=pseudo)\) differential operator of order 1-0 is also a microdifferential operator and its symbol can be written in the form of exponential function of a symbol of order 1-0 which is constructed from a given operator.
scientific article; zbMATH DE number 3849752