About TRACE

[Henry Lieberman <lieber@media-lab.media.mit.edu>]

   Notice the "(declare (noinline fact))" on page 255 of the manual?
   Well include something like it for flatten in your definition above
   and it will work.  

It is really too bad that MCL is by default in a mode which
effectively renders useless the debugging tools like TRACE and STEP.
Beginners will naively attempt to use the debugging tools and not
be able to understand why they don't work.  You will be constantly
answering this kind of bug report.  Putting in explicit declarations
for every function you want to trace is a pain.  It should either be
in "debugging mode" by default and have to set switches in order to 
increase speed, or at least have a single-switch "debugging mode" [perhaps
this is *compile-defintions*?] and make clear the requirement that
definitions be reloaded when the debugging mode is set [by having warnings
printed when debug mode is turned on, and also perhaps the first time trace
or step is called when debug mode is off].