1. V. N. Branets and I. P. Shmyglevskii, The Use of Quaternions in Problems of Rigid Body Orientation [in Russian], Nauka, Moscow (1992).
2. Yu. A. Gladyshev, Beltrami–Bers Formalism and Its Applications to Mathematical Physics [in Russian], Kaluga State Univ. Press, Kaluga (1997).
3. G. C. Moisil, “Sur les quaternions monogenes,” Bull. Sci. Math., II Ser, 55, 168–174 (1931).
4. R. Fueter, “Zur Theorie der regulären Funktionen einer Quaternionenvariablen,” Monatsh. Math. Phys. 43, 69–74 (1936).