[1] M. Abrate, Quadratic Formulas for Generalized Quaternions, The Journal of Algebra and its Applications, Vol. 8, Issue 3, pp. 289-306, 2009.
[2] M. Abrate, The Roots of a Generalized Quaternion, Congressus Numeratium, Vol. 201, Jan. 2010, 179-187 (Winnipeg, Canada)