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I was calculating some amplitudes and I end up with an expression like this:

$$(\bar{c}\gamma^\mu\gamma^\nu\gamma^\rho P_L b)(\bar{d}\gamma_\mu\gamma_\nu\gamma_\rho P_L u)$$

In the solution of the exercise they say that, from the Fierz identity:

$$(\bar{c}\gamma^\mu\gamma^\nu\gamma^\rho P_L b)(\bar{d}\gamma_\mu\gamma_\nu\gamma_\rho P_Lu)=16(\bar{c}\gamma^\mu P_L b)(\bar{d}\gamma_\mu P_L u)$$

How can I show that?

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# A Fierz identity

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