Good evening,
In differential forms (in the proof of the naturality of the exterior derivative), I don't get why if $h\in \Lambda^0(U)$ and $f^*$ is the pullback then,
$f^*dh=d(f^*h)$.
I wrote $dh=\frac{\partial h}{\partial x^i}dx^i$ so (?) $f^*dh(v)=\frac{\partial h}{\partial f^i}df^i(df(v))$ but I don't know if this is correct and I can't continue...
Thanks a lot for your help