KovalevY. G. “On the Criteria of Transversality and Disjointness of Nonnegative selfadjoint extensions of Nonnegative Symmetric Operators”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 70, no. 4, Apr. 2018, pp. 495-0, https://umj.imath.kiev.ua/index.php/umj/article/view/1571.