Extensions of symmetric relations

Maximal accretive and dissipative extensions of symmetric relations defined by abstract boundary conditions are considered in Hilbert space. Under the assumption that the resolvent of some extension has properties such as belonging to the Neumann–Shatten ideal or having given asymptotics of the $s$-numbers, either sufficient or necessary and sufficient conditions are found for a perturbation of the boundary conditions guaranteeing that the above properties are preserved for the resolvent of the perturbed extension.