Iterates of systems of operators in spaces of   $\omega$-ultradifferentiable functions
  Given two systems $P=(P_j(D))_{j=1}^N$ and $Q=(Q_j(D))_{j=1}^M$ of linear partial differential operators with constant coefficients, we consider the spaces ${\mathcal E}_\omega^P$ and ${\mathcal E}_\omega^Q$ of $\omega$-ultradifferentiable functions with respect to the iterates of the systems $P$ and $Q$ respectively. We find necessary and sufficient conditions, on the systems and on the weights $\omega(t)$ and $\sigma(t)$, for the inclusion ${\mathcal E}_\omega^P\subseteq{\mathcal E}_\sigma^Q$. As a consequence we have a generalization of the classical Theorem of the Iterates. 
Chiara Boiti, Rachid Cha\"ili, Tayeb Mahrouz
math.FA