Mazorchuk, V., M. Ponomarenko, and L. Turowska. “Some Associative Algebras Related to $U(\mathfrak g)$ and Twisted Generalized Weyl Algebras”. MATHEMATICA SCANDINAVICA, vol. 92, no. 1, Mar. 2003, pp. 5-30, doi:10.7146/math.scand.a-14392.