A bound for the eigenvalue counting function for Krein-von Neumann and Friedrichs extensions (Q329523)

The authors derive upper estimates for the eigenvalue counting function \(N(\lambda)\) of the Krein-von Neumann extension and the Friedrichs extension of a symmetric, closed, and strictly positive partial differential operator of order \(2m\) acting on \(L^2(\Omega)\), where \(\Omega\) is a bounded domain of \(\mathbb{R}^n\) without any regularity assumptions on its boundary (the operator is an \(m\)-th power of a second-order operator). Apart from its interesting results, the paper is also well written and educational.