I want to make a symbol for "maps isomorphically" which consists of a relatively large tilde above a right arrow. Overset doesn't work (besides, the tilde would be too small). MWE:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Thus $X$ is isomorphic to $Y$ via $f$:
\[f : X \overset{\tilde}{\to} Y.\]
\end{document}
I also tried using array but that didn't work either. MWE:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Thus $X$ is isomorphic to $Y$ via $f$:
\[f: X \begin{array}{c}\tilde \\ \to \end{array} Y\]
If I could get this to work, the spacing would need to be adjusted significantly.

ooalign, one ofegreg's favourite tools - a tutorial can be found in \subseteq + \circ as a single symbol ("open subset") and in many answers since :) – cmhughes Aug 12 '14 at 21:18\xrightarrow{\sim}? – Alex Nelson Aug 12 '14 at 21:32