Fourier transform over a local field (source code)

= Fourier transform over a local field
{title2=$\widehat f(y)=\int_Ff(x)\psi(xy)\,dx$}

For a <local field> $F$, an <additive character> $\psi$, and a <Haar measure> $dx$, the Fourier transform is
$$
\widehat f(y)=\int_Ff(x)\psi(xy)\,dx.
$$
It maps the <Schwartz-Bruhat space> to itself.