1. Split quaternions and the Dirac equation;Antonuccio;Advances in Applied Clifford Algebras,2015
2. Preliminary sketch of bi-quaternions;Clifford;Proceedings of the London Mathematical Society,1873
3. Preliminary sketch of bi-quaternions;Clifford,1882
4. Quaternionic analysis, representation theory and physics;Frenkel;Advances in Mathematics,2008