A cheap way to closed operator sums

Bernhard H. Haak, Peer Christian Kunstmann

Let $A$ and $B$ be sectorial operators in a Banach space $X$ of angles $\ddot{I}{‰}_A$ and $\ddot{I}{‰}_B$, respectively, where $\ddot{I}{‰}_A+\ddot{I}{‰}_B<\ddot{I}€$. We present a simple and common approach to results on…