@article{Kovalev_2018, title={On the criteria of transversality and disjointness of nonnegative selfadjoint extensions of nonnegative symmetric operators}, volume={70}, url={https://umj.imath.kiev.ua/index.php/umj/article/view/1571}, abstractNote={We propose criteria of transversality and disjointness for the Friedrichs and Krein extensions of a nonnegative symmetric operator in terms of the vectors $\{ \varphi j , j \in J\}$ that form a Riesz basis of the defect subspace. The criterion is applied to the Friedrichs and Krein extensions of the minimal Schr¨odinger operator $\scr A$ d with point potentials. We also present a new proof of the fact that the Friedrichs extension of the operator $\scr A$ d is a free Hamiltonian.}, number={4}, journal={Ukrains’kyi Matematychnyi Zhurnal}, author={Kovalev, Yu. G.}, year={2018}, month={Apr.}, pages={495-505} }