Kovalev, Yu. G. 2018. “On the Criteria of Transversality and Disjointness of Nonnegative Selfadjoint Extensions of Nonnegative Symmetric Operators”. Ukrains’kyi Matematychnyi Zhurnal 70 (4): 495-505. https://umj.imath.kiev.ua/index.php/umj/article/view/1571.