Set and export an environment variable RLMMA to your executable
text-based Mathematica.

For instance, on Mac OSX this is
/Applications/Mathematica.app/Contents/MacOS/MathKernel, which is used as
a default when RLMMA is not set.

When the call to Mathematica fails in PSL-based Reduce, it can happen
that you fall through into the underlying Lisp: If you obtain a prompt
like "1 lisp>", then exit the session using the following command w/o
the quotes: "(quit)".
