@article{Kovalev_2018, title={On the criteria of transversality and disjointness of nonnegative selfadjoint
extensions of nonnegative symmetric operators}, volume={70}, url={http://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 SchrÂ¨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={Ukrainsâ€™kyi Matematychnyi Zhurnal}, author={KovalevYu. G.}, year={2018}, month={Apr.}, pages={495-505} }