Solution
= Solution
The <Fourier transform of a derivative> gives
$$
\widetilde g(k)=\widetilde{p'}(k)=ik\widetilde p(k).
$$
Hence
$$
\boxed{\widetilde p(k)=\frac{\widetilde g(k)}{ik}}
$$
for $k\ne0$. The assumed existence of the transforms excludes an arbitrary nonzero constant in $p$.