The symbol for a map which is an isomorphism?

Suppose I have a map $A\rightarrow B$ which is an isomorphism. So I'd like to have smth like: \rightarrow and \simunder it. I could try \underset{}_{}, but there is certainly a ready made symbol?

I couldn't find the symbol in Detexify service, neither in the comprehensive list of LaTeX symbols.

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You want the \sim under the \to? Odd. I don't think I've ever seen an isomorphism written like that. –  TH. Oct 26 '10 at 2:38
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2 Answers

Theoretically, you could use \xrightarrow[\sim]{} (from amsmath) or \xlongrightarrow[\sim]{} (from extarrows). Both look horrible though. The \sim on top of the arrow (like \xlongrightarrow{\sim}) looks somewhat better.

Unicode defines ⥴ (U+2974 RIGHTWARDS ARROW ABOVE TILDE OPERATOR), which you can use in case you run Xe/LuaLaTeX with unicode-math (either directly or with the \rightarrowsimilar alias). There are also ⥱ (\equalrightarrow), ⥲ (\similarrightarrow), ⥳ (\leftarrowsimilar), ⥵ (\rightarrowapprox) and other strange things.

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Thanks a lot for the comments! For me \xrightarrow{\sim} is quite enough. –  qui_vadis Oct 26 '10 at 19:53
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A bit of adjustment of the spacing may help. For example, with

\documentclass{article}
\usepackage{amsmath,fixltx2e}
\newcommand*\MapsTo{%
\xrightarrow[\raisebox{0.25 em}{\smash{\ensuremath{\sim}}}]{}%
}
\begin{document}
Test $$x \MapsTo y$$ test.
\end{document}


I feel the result is not tool bad. You may need to adjust the amount of vertical shift to suite the font in use. I've not scaled-down the \sim here, as it's not clear from the original question if it should be full-sized or small. It would be easy enough to do that, though, if necessary.

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