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3. H. Graßmann: Die Wissenschaft der extensiven Größe oder die Ausdehnungslehre (Wigand, Leipzig 1844)
4. J.M. McCarthy: Introduction to Theoretical Kinematics (MIT Press, Cambridge 1990)
5. W.K. Clifford: Preliminary sketch of bi-quarternions, Proc. Lond. Math. Soc. 4, 381–395 (1873)