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I have a construction that isn't a function, but does produce values assigned (in an ill defined way) varyingly over a domain. I can write this as A \leadsto B. I want to write what happens to a \in A not as a \mapsto b but with a \leadsto arrow that begins with the small vertical bar \mapstochar. I've already loaded the extpfeil package, so stmaryrd won't work. What can I do?

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1 Answer 1

up vote 3 down vote accepted

Use \mapstochar and \leadsto, that's simple! With just a small correction for hiding the bump.

\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}

$a\mapstochar\mathrel{\mspace{0.45mu}}\leadsto b$

\end{document}

Of course you'll want to define a macro for it:

\newcommand{\foo}{\mapstochar\mathrel{\mspace{0.45mu}}\leadsto}

enter image description here

If you load latexsym rather than amssymb, then more spacing is needed

\documentclass{article}
\usepackage{amsmath,latexsym}
\begin{document}

$a\mapstochar\mathrel{\mspace{1.75mu}}\leadsto b$

\end{document}

enter image description here

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What if I wanted to make it extensible? I didn't initially, but that's how I started trying to do it, because extpfeil has a syntax for creating arrows, so now I want to know. –  jdc Aug 31 at 8:55
    
It doesn't work for me for some reason. Something's misaligned. Worse, the difficulty mysteriously doesn't improve when I change the mspace. tinypic.com/r/2q0q87s/8 –  jdc Aug 31 at 9:04
    
It seems you're loading latexsym rather than amssymb. Use \mspace{1.75mu} –  egreg Aug 31 at 16:11
    
Beautiful! Thank you! But why didn't changing the spacing by a smaller amount do anything? –  jdc Aug 31 at 16:15
1  
@jdc mu is a tiny unit: 1/18 of an em –  egreg Aug 31 at 16:19

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