- #1
Replusz
- 142
- 14
- TL;DR Summary
- I don't understand what is happening from line 1 to 2.
It looks like he is taking out the derivative operator from the commutator.
Which I presume is not allowed?
Or he could be using product rule on commutator and then neglecting the 2nd part (maybe because it is trivially 0? I don't see why it is 0 tho: it is [nabla, Pi]Phi )