Kovalev, Yu. 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 April 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1571.