[dev-context] My way on matharrows

[Taco Hoekwater]

Aditya Mahajan wrote:
> Hi,
> 
>  I am attaching myway on using matharrow. Are there any suggestions 
> before I release it to public?
> 
> I found some surprises while making this my way.
> 
> 1. Somewhere along the line of development, \xrightarrow{text} changed 
> to placing text at the bottom of the arrow (rather than the top as in 
> amstex). This is not a bug, just something that works differently. 
> Should this be changed? These arrow definitions are pretty new, so I do 
> not think that a change at this stage will effect too many users. It may 
> not be possible to change later for compatibility reasons.

In the interest of porting stuff from amstex, changing the behaviour is
probably better.

> 2. Something goes wrong with palatino (used by mag-01). Have a look at 
> the \xmapsto and \xrightleftharpoons and \xleftrightharpoons in the pdf. 
> \xmapsto can be corrected by changing its defintion to
> 
> \definematharrow [xmapsto]            [3599] [\mapstofill]
> 
> Basically, providing a bit more cusion on the left, so that the middle 
> \relbar not overlap the \mapstochar.
> 
> Should this definition go to math-ext.tex or to something specific to 
> palatino. I have not tested with other fonts, but what is the general 
> strategy when definitions differ for different fonts?

something should be possible with mathcollections, I guess?
(Hans knows this better then I do)

> I could not correct leftrightharpoons. Why does this not work?
> 
> \definematharrow [xleftrightharpoons] [3395,3359] 
> [\leftharpoonupfill,\rightharpoondownfill]

Because the current definition of dodoxmtharrow does not like it
when the second arg starts with two identical digits. Changing
it to this fixes the problem:

   \def\dodoxmtharrow[#1,#2,#3][#4,#5,#6][#7]#8#9%
   {\edef\tempa{#2}\ifx\tempa\empty %TH changed line
      \mathrel{\domthxarrsingle{#7}{#1}{#4}{#8}{#9}}%
    \else
      \mathrel{\domthxarrdouble{#7}{#1}{#2}{#4}{#5}{#8}{#9}}%
    \fi}