In the first edition of Griffiths' Introduction to Elementary Particles, p. 129, I read: "In strong interactions, charge conjugation invariance requires, for example, that the energy distribution of the charged pions in the reaction p + p_bar -> [tex]\pi^+[/tex] + [tex]\pi^-[/tex] + [tex]\pi^0[/tex] should (on average) be identical." Griffiths gives reference C. Baltay et al, .Phys Rev Lett 15, 591, (1965). I looked it up. This paper appears to only uses the argument, it does not explain its origin. Could someone please explain how C-symmetry makes a prediction about the distribution in pion energies in this case? Does this example hint at a broader principle which makes a statement about the energy distribution of reaction products in the final state of a strong interaction which respects C-symmetry? Thanks!