1. E. Recami andR. Mignani:Lett. Nuovo Cimento,4, 144 (1972). This paper will be referred to in the following as « paper I ». See alsoV. S. Olkhovsky andE. Recami:Lett. Nuovo Cimento,1, 165 (1971).
2. After the completion of paper I, we became aware of the existence of papers (2–4), which approached our problem too. Criticizing ref. (2) is the content of ref. (3). Paper (4), byAntippa, puts forward a theory yielding the same results as Parker’s (7), both works being confined tobidimensional space-time. The original features of ref. (4),i.e. introducing unidirectionality in time for bradyons and in space for tachyons, seems extraneous to our own philosophy.
3. J. G. Gilson:Mathem. Gazette,52, 162 (1968). See previous footnote.
4. S. Naranan:Lett. Nuovo Cimento,3, 623 (1972). See previous footnote.
5. A. F. Antippa:A one-dimensional causal theory of tachyons, preprint UQTR-TH-3, University of Quebec (Trois Rivieres, 1971). See previous footnote. In a preceding paper (5),Antippa andEverett went back to Feinberg’s philosophy (6), taking advantage of the fact that Lorentz-covariance violation implicit in it does not come out in a bidimensional space-time.