Ostrovskii, V. L., and Y. S. Samoilenko. “On Spectral Theorems for Families of Linearly Connected Self-Adjoint Operators With Given Spectra Associated With Extended Dynkin Graphs”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 11, Nov. 2006, pp. 1556–1570, https://umj.imath.kiev.ua/index.php/umj/article/view/3554.