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This is not really a physical question, but it relates to notation in QED.

The ${\gamma}^5$ matrix is defined as

$${\gamma}^5=i{\gamma}^0 {\gamma}^1{\gamma}^2{\gamma}^3$$

Wouldn't it be more logical to write ${\gamma}^5$ as ${\gamma}^4$?

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From Wikipedia;

Although $\gamma ^{5}$ uses the letter gamma, it is not one of the gamma matrices of Cl1,3(R). The number 5 is a relic of old notation in which $\gamma ^{0}$ was called "$\gamma ^{4}$".

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