## Why is 3 pion decay of eta (η) strong forbidden?

I have read that 3 pion decay of the eta is not allowed as a strong reaction, but proceeds as an electromagnetic interaction. I do not see why it is strong forbidden.
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 Recognitions: Science Advisor That is easiest to see using G parity, which is $$C e^{i\pi I_y}$$. One or three pions have negative G, while the eta has positive G.
 How do you find the result of the I2 rotation operation?

Recognitions: