On inverses of Krein's Q-functions

Claudio Cacciapuoti, Davide Fermi, Andrea Posilicano

Let $A_Q$ be the self-adjoint operator defined by the $Q$-function $Q:z\mapsto Q_z$ through the Krein-like resolvent formula $$(-A_{Q}+z)^{-1}= (-A_{0}+z)^{-1}+G_{z}WQ_{z}^{-1}…