KovalevYu. G. “On the Criteria of Transversality and Disjointness of Nonnegative selfadjoint extensions of Nonnegative Symmetric Operators”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 4 (April 25, 2018): 495-505. Accessed December 2, 2020. http://umj.imath.kiev.ua/index.php/umj/article/view/1571.