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**To**:*math-font-discuss@cogs.susx.ac.uk***Subject**:**Arrow heights****From**:*alanje@cogs.susx.ac.uk (Alan Jeffrey)***Date**: Fri, 20 Aug 93 15:41 BST

I've been looking at the arrows in cm* and ms*, and in particular how accent positioning works with arrows. In doing so, I've discovered some interesting facts about the AMS arrows: * The heights of the single arrows are very different. In increasing order of height we have: * \rightarrow = \rightharpoonup = \rightharpoondown * \rightsquigarrow * \twoheadrightarrow = \rightarrowtail * \multimap = \looprightarrow This produces fairly odd results if you use \mathop superscripts to put labels onto arrows, see the accompanying test document. * The \leftrightarrows aren't vertically centered. * There's a vast disparity in the amount of vertical space around the arrows. Compare \rightarrow with \twoheadrightarrow for example. For limit and accent positioning, it might be nice to include some restrictions on the allowed heights for arrows. I was thinking of breaking the arrows into five sizes: * All the single arrows (\rightarrow, \rightharpoonup, \rightharpoondown, \rightsquigarrow, \twoheadrightarrow, \rightarrowtail, \multimap and \looprightarrow etc.) must be the same height. * All the double arrows (\Rightarrow etc.) must be the same height. * All the triple arrows (\Rrightarrow etc.) must be the same height. * All the two-arrows (\rightrightarrows, \leftrightarrows etc.) must be the same height. * All the two-harpoons (\leftrightharpoons) must be the same height. Are these reasonable restrictions? Is there some good reason for the AMS arrows being different heights? Should we split up some of these classes (it's not obvious what to do with \looparrowright for example)? Should we collapse some of these classes (the two-arrows and the triple-arrows perhaps)? Should we be worried abut not being upwardly compatible with the current arrows? Alan. --- cut here for test document --- \documentstyle{article} \font\msam=msam10 \textfont15=\msam \mathchardef\rightsquigarrow"3F20 \mathchardef\twoheadrightarrow"3F10 \mathchardef\rightarrowtail"3F1A \mathchardef\looprightarrow"3F23 \mathchardef\Rrightarrow"3F56 \mathchardef\rightrightarrows"3F1C \mathchardef\leftrightarrows"3F13 \mathchardef\leftrightharpoons"3F0B \mathchardef\multimap"3F28 \def\doarrows{ \do\rightarrow \do\rightharpoonup \do\rightharpoondown \do\rightsquigarrow \do\twoheadrightarrow \do\rightarrowtail \do\multimap \do\looprightarrow \do\Rightarrow \do\Rrightarrow \do\rightrightarrows \do\leftrightarrows \do\leftrightharpoons } \fboxsep=0pt \begin{document} $$ \def\do#1{\fbox{$#1$}} \doarrows $$ $$ \def\do#1{\mathop{#1}\limits^x} \doarrows $$ \end{document}

**Follow-Ups**:**Re: Arrow heights***From:*bbeeton <BNB@MATH.AMS.ORG>

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