I think I'm done. Forget everything or keep it in mind for the next stupid
one :-)
>$$x \mapsto \left\{
> \begin{array}{ll}
> 1 & \text{ if } x > 0\\
> \uparrow & \text{ elsewise}
> \end{array}\right.
>$$
^^
Here's the solution. Using the old TeX stylish $$ for display formulae make
that formula blue, replaced it by \[ and \] makes everyhting green. I try
to change to the correct LaTeX stylish commands for years, but now i have a
reason to try it more seriously. On the other hand i'll keep that in mind
for making formulae blue :-)
Thanks a lot, your example led me the way.
hs