1. S. Annin, J. Algebra Appl. 3(2), 193–205 (2004).
2. V. K. Bhat, Beitr. Algebra Geom. 49(1), 277–283 (2008).
3. V. K. Bhat, Int. J. Algebra Comput. 20(3), 457–463 (2010).
4. C. Faith, Comm. Algebra 28, 3983–3986 (2000).
5. D’Apres J. Dixmier. In Seminaire Bourbaki, Lecture Notes Math.;P Gabriel,1968