"These three invariances are not independent. In the framework of local field theory, invariance under proper leads to the invariance of all interactions under combined operations CPT, where C is the charge conjugation operator, changing particles to antiparticles, P, the parity space inversion operator, changing \overline{r} to -\overline{r}, and T is the time reversal operator, changing t to -t. The equality of the masses and lifetimes of the particles and their antiparticles follows from this theorem."