# [Om] invisible times and invisible plus

Jan Willem Knopper jknopper at win.tue.nl
Mon Aug 31 14:23:36 CEST 2009

```Dear all,

Is there a way to describe in OpenMath that a certain times or plus
symbol is invisible ?

For invisible times this would be something like 2a or 2(x+1) and for
invisible plus I'm thinking about 1 1/2 (= 3/2).

A lot of this has to do with presentation, but one might also argue that
numbers like 1+1/2 and 1 1/2 have different semantic meaning in primary
or highschool, where the integer part is written in front of the fraction,
rather than writing 3/2.

Furthermore, for invisible plus, the use of the symbol would be
binary, with as the first argument a positive integer (or maybe a
variable) and as the second argument a fraction (of positive integers,
or maybe variables).

In the MathDox Formula Editor I would like to let the user input
expressions with invisible times and invisible plus and it would be nice
to be able to store the information that they are invisible (especially
for invisible plus).

Does anyone know how to describe expressions like 1 1/2 in OpenMath?