# Lie Algebra of the Lorentz group - a weird notation?

In Srednicki's text on quantum field theory, he has a chapter on quantum Lorentz invariance. He presents the commutation relations between the generators of the Lorentz group (equation 2.16) as follows:
$$[M^{\mu\nu},M^{\rho\sigma}] = i\hbar\Big(g^{\mu\rho}M^{\nu\sigma}-(\mu\leftrightarrow\nu)\Big)-(\rho\leftrightarrow\sigma)$$
I have never seen the strange double-arrow notation in any linear algebra book before. Is this notation at all standard and if so, what does it mean?

ShayanJ
Gold Member
It just means "its the same thing as the last term, just put $\mu$ instead of $\nu$ and vice-versa." The same about the last parenthesis.

haushofer