On ultra wave front sets and Fourier integral operators of infinite order
The authors define pseudodifferential and Fourier integral operators acting on ultradistributions. They give a propagation theorem (in the framework of ultra wave front sets) for Fourier integral operators of infinite order. As a consequence they obtain propagation of ultra wave front sets for solutions of Cauchy problems for some hyperbolic operators with variable multiplicity.
Fourier integral operators of infinite order
scientific article; zbMATH DE number 4205026