1. F. Lurcat andL. Michel:Nuovo Cimento,21, 574 (1961).
2. For the use of the complex Lorentz group (2) see, for example,R. Jost: inTheoretical Physics in the 20th Century, edited byM. Fierz andF. Weisskopf (New York, 1960) orA. S. Wightman: inDispersion Relations and Elementary Particles, EditorsC. de Witt andR. Omnės (New York, 1960).
3. Journ. Math. Phys., (to be published).
4. This is an example of the known fact that to a given complex Lie algebra there may correspond more than one real Lie algebra (L. Pontrjagin:Topological Groups (Princeton, N. J., 1958), p. 265).
5. K. Yano andS. Bochner:Curvature and Betti Numbers, Chapter VII (Princeton, N. J., 1953).