Superposition and propagation of singularities for extended Gevrey   regularity
  We use sequences which depend on two parameters to define families of ultradifferentiable functions which contain Gevrey classes. It is shown that such families are closed under superposition, and therefore inverse closed as well. Furthermore, we study partial differential operators whose coefficients satisfy the extended Gevrey regularity. To that aim we introduce appropriate wave front sets and derive a theorem on propagation of singularities. This extends related known results in the sense that weaker assumptions on the regularity of the coefficients are imposed. 
Stevan Pilipovi\'c, Nenad Teofanov, Filip Tomi\'c
math.FA math.AP