[Om] invisible times and invisible plus

Professor James Davenport jhd at cs.bath.ac.uk
Mon Aug 31 17:06:15 CEST 2009

On Mon, August 31, 2009 2:09 pm, Christoph LANGE wrote:
> Dear Jan Willem,
> 2009-08-31 14:23 Jan Willem Knopper <jknopper at win.tue.nl>:
>> Is there a way to describe in OpenMath that a certain times or plus
>> symbol is invisible ?
> AFAIK there is no standard way, and IMHO there should not be a standard
> way.
> I think there are two nonstandard solutions, one of which should be chosen
> as appropriate for the particular application:
> 1. define a special OpenMath symbol not just for the "invisible plus" in a
>    mixed fraction, but a specific constructor for the mixed fraction.
I'm very happy with this - it cound either go in a new 'nums2', or
possibly in a 'schoolmaths' CD - depending really on whether you see this
as part of a bigger package. The FMP is pretty obvious, and I'll leave it
to Paul to write the corresponding .ntn files. If some-one wants to write
the CD, I'll happily start the acceptance process on it, since it's
clearly wanted by several people. I gues mixed_fraction is the obvious
symbol name.
>    (Compare James' favorite landau-in example, where he also introduces a
>    completely new symbol.)
Flattery will get you everywhere!
> 2. use the normal plus, but annotate the whole expression with some
>    information that causes the renderer to render the plus invisibly.
> 1. could look like
> 2. could look like
>   <OMATP>
>     <OMS cd="my" name="preferred-presentation"/>
>     <OMS cd="my" name="mixed-number"/>
>   </OMATP>
>   <OMA>
>     <OMS cd="arith1" name="plus"/>
>     <OMV name="whole"/>
>     <OMA>
>       <OMS cd="arith1" name="divide"/>
>       <OMV name="num"/>
>       <OMV name="dem"/>
>     </OMA>
>   </OMA>
Possibly, if one sees the presentation as being at this level.
> I could imagine a more sophisticated attribution with the context-related
> stuff developed by my colleagues, see Kohlhase/Müller/Rabe MKM 2008.
Indeed so. However, there is a more fundamental point - we DO want to
answer Jan's actual question, and many related ones, e.g. I want a group
but the operator is to be written as \circ, and so on.

I suspect we want to be able to write
    <OMS cd="presentation_hacks" name="use_symbol"/>
    <OMFOREIGN encoding="MathML-Presentation">
      <math xmlns="http://www.w3.org/1998/Math/MathML">
  <OMS name="plus" cd="arith1"/>

or some such.
James Davenport
Recently: Visiting Full Professor, University of Waterloo
Now back as:
Acting Head of Department, Computer Science,
Hebron & Medlock Professor of Information Technology and
Chairman, Powerful Computing WP, University of Bath
OpenMath Content Dictionary Editor and Programme Chair, OpenMath 2009
IMU Committee on Electronic Information and Communication

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