@0ßelö7 I've been spending some time on this i.imgur.com/XrBEKuR.png

I already proved (i) and the lemma and then I just need to scribble out applying it to the product rule and I think that's it

@GPhys no

@GPhys how did you find the $H^\mu$'s?

That's a nontrivial lemma

@0ßelö7 $H_\mu=\int_0^1\frac{\partial f}{\partial y^\mu}\,\mathrm{d}t$ where $y^\mu=t(x^\mu-x^\mu_p)+x^\mu_p$

(I just "guessed")

the generalization from one coordinate was obvious enough

huh, ok

@GPhys so what is the issue?

@GPhys how could I put a bar on $\mathrm d$ like on $\hbar$?

@0ßelö7 nothing, for that one

@0ßelö7 I think hbar is defined within latex as a function of h itself, so we should be able to find its definition.......

\newcommand{\hbar}{\mathchar'26\mkern-9mu h}

$$\mathchar'26\mkern-9mu{\mathrm d}$$

hmm

oh well, guess I just won't write that equation

it would be overkill anyway