Beyond the Einstein Addition Law and its Gyroscopic Thomas ...
Abraham A. Ungar
An introduction to the theory of groups. Springer-Verlag, New York, fourth edition, 1995. Krzysztof Rózga. On central extensions of gyrocommutative gyrogroups. Pacific J. Math., 193(1):201–218, 2000. Arlan Ramsay and Robert D. Richtmyer.