Kuznetsova, Victoriya. 2011. “MODEL REPRESENTATIONS OF THE LIE ALGEBRA $[A_2, A_1] = iA_1$ OF LINEAR NON-SELFADJOINT OPERATORS”. Ann. Sofia Univ. Fac. Math. And Inf. 100 (December):93-112. https://annual.uni-sofia.bg/index.php/fmi/article/view/248.