Horozov, E. “AUTOMORPHISMS OF ALGEBRAS AND BOCHNER‘S PROPERTY FOR DISCRETE VECTOR ORTHOGONAL POLYNOMIALS”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 104, Dec. 2017, pp. 23-38, https://stipendii.uni-sofia.bg/index.php/fmi/article/view/35.