# Re: More on subscripts and superscripts

• To: math-font-discuss@cogs.susx.ac.uk
• Subject: Re: More on subscripts and superscripts
• From: alanje@cogs.susx.ac.uk (Alan Jeffrey)
• Date: Fri, 13 Aug 93 19:00 BST

```>Arrows and glyphs?  Having experimented with various composite arrows (and
>\kerned myself silly in the process) and seen them fall apart from time to
>time, I would want everything as a single glyph (okay, but you know what I
>mean).

What I was hoping to do was move the problem of kerning from the macro
writer to the font implementor, so its the font implementor's job to
<leftrightarrow>, by whatever means necessary, be it glyph shape,
kerning or ligaturing.  But there are problems about the glyphs
breaking up, which is why I was asking about dvi driver digitization.

>From JMR's response, I think the answer is that a `conformant' dvi
driver should never break up a short arrow.  Very long arrows may end
up with kerning in them, so it's up to the font implementor to make
sure that there's enough leeway in the extension glyphs that there'll
never be gaps in a long arrow.  TeX currently sometimes produces gaps,
for example I've seen \longrightarrow come out with a small gap
between the - and the rightarrow.  I don't know if this was due to a
dodgy dvi driver though...

Alan.

```