L. Vavrykovych, O. Shapovalova, and S. A. Kuzhel, “On $J$-self-adjoint extensions of the Phillips symmetric operator”, MFAT, vol. 16, no. 4, pp. 333–348, Dec. 2010, Accessed: Feb. 04, 2026. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/461