Let $f_n$ be a sequence of differentiable functions on $[0, 1]$ with
- $f_n \to f$ uniformly for some (necessarily) continuous $f$.
- $f'_n - g \to 0$ in $L^{\infty}$ for some measurable $g$.
Is it true that $f$ is differentiable with $f' = g$ almost everywhere?
Some comments: An almost everywhere version of the same question is answered negatively here. I expected to have an easy affirmative answer if $f$ are assumed instead everywhere differentiable, but to my surprise this seems to be much more subtle. Note that we do not assume that $f’_n$ are in $L^1$, nor that $f_n$ are absolutely continuous, so that the fundamental theorem of calculus does not apply.