1. Levels of quaternion algebras;D. Hoffmann;Archiv der Mathematik (Basel),2008
2. A quaternion algebra of sublevel 3;M. Krüskemper;Bulletin of the Belgian Mathematical Society Series B,1991
3. T.Y. Lam, Introduction to quadratic forms over fields, Graduate Studies in Mathematics no. 67, American Mathematical Society, Providence, RI, 2005.
4. Levels of division algebras;D. Leep;Glasgow Mathematical Journal,1990
5. Levels and sublevels of division algebras;D. Lewis;Proceedings of the Royal Irish Academy Section A,1987