# Dirac trace theorem

I am unable to prove exactly one trace identity that appears in the appendix of Peskin and Schroeder's QFT book. Can someone help me?

The theorem [Appendix A.4 eqn (A.28)] says that the order of $\gamma$ matrices inside of a trace can be reversed:

$$\text{tr}(\gamma^\mu\gamma^\nu\gamma^\rho\gamma^\sigma\cdots)=\text{tr}(\cdots\gamma^\sigma\gamma^\rho\gamma^\nu\gamma^\mu)$$

Can someone help me with this trivial thing...?

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