@johncarlosbaez Is it worth mentioning that C and T commute? (Or maybe there are weird cases where they don't?) And, if I understand things right, in particle physics C and P also commute but P and T anticommute?

@johncarlosbaez Apparently quantum field theorists have chosen to live in (-,-,-), which is neat because then P and T can be associated with quaternions, but weird because I don't think it corresponds to either Pin(1,3) or Pin(3,1), but rather to one of the other Pin groups double covering O(1,3). This stuff is pretty fascinating, and getting me more interested in finite groups.

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