[dev-context] overrightarrow and underrightarrow give the same result

[Hans Hagen]

On 25-10-2012 14:12, luigi scarso wrote:
> $\overrightarrow{ab}$
> $\underrightarrow{ab}$
>
> both give the same result  ($\underrightarrow{ab}$)

a few under/over mixups in math-arr.mkiv: line 429 and 434

Question for Aditya:

We have this arrow module, but as luatex has better under / over fill 
support, we could use:

% \unexpanded\def\underrightarrow#1{\mathop{\Uunderdelimiter 
\defaultmathfamily "2192 {#1}}}
% \unexpanded\def\overrightarrow #1{\mathop{\Uoverdelimiter 
\defaultmathfamily "2192 {#1}}}

which actually gives a different spacing. So the question is: how valid 
is the arrow module?

btw, The old kludges wrt left/right arrow fills with text above as used 
in chemical reactions is solved using virtual characters ... I discussed 
this with Gyre Math Font Gurus and we agreed that it makes sense to have 
such double arrow combination snippets in the fonts ... it was also 
discussed that we should have a well defined private space in unicode 
for additional characters)

Hans

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