Berezansky, Yu. M., and M. E. Dudkin. “The Direct and Inverse Spectral Problems for the Block Jacobi Type Unitary Matrices”. Methods of Functional Analysis and Topology, vol. 11, no. 4, Dec. 2005, pp. 327-45, https://zen.imath.kiev.ua/index.php/mfat/article/view/291.