1. A. Staruszkiewicz:Acta Phys. Pol.,29, 249 (1966). It should be noted that the theorem is not new at all. It is contained in Einstein's derivation (see for exampleW. Pauli:Theory of Relativity, p. 126). In our paper we have formulated Einstein's reasoning in a covariant notation.
2. W. Pauli:Theory of Relativity, (London, 1958), p. 134.
3. H. Arzeliès:Nuovo Cimento,35, 792 (1965);41 B, 81 (1966).
4. A. Gamba:Nuovo Cimento,37, 1792 (1965).
5. T. W. B. Kibble:Nuovo Cimento,41 B, 72 (1966).