[Maxima] Bug in derivabbrev? in defrule?

[Richard Fateman]

Martin Schönecker wrote:
> Hi,
>
> judging from what the maual says about derivabbrev, I think it should 
> affect only the way expressions are displayed, and not affect calculations.
>   

It does affect only the way expressions are displayed.  You encountered 
a bug in the display program.
The program should display

  aa
    bb bb bb bb bb bb ....   bb

where there is a string of length cc   of the symbol bb.

So it has to count from cc down to 0.  Since cc is not an integer, there 
is a problem.

Now how to fix this?   What would you like to see?  perhaps

  aa
    <cc>
   bb

or an error message?
or ??

The code is open for inspection and repair.
RJF