Discrete symmetries and the einstein principle of relativity

It is possible to limit the field of the data exchanged by observers so that discrete symmetry principles of a new kind could be valid. The decay of the K⁰_L into two pions exhibits such a symmetry. Some other consequences, unfortunately difficult to test, are presented. One of the main results is that the weak interactions should possess symmetries which correspond to TP and TC in addition to CP, but TCP is not necessarily a symmetry.