A reference for a list of 100 at least challenging problems has been
added to the 'unknown' chapter in the Structure Determination from
Powder Diffraction - Database (SDPD-D) :
http://fluo.univ-lemans.fr:8001/iniref/unknown.html
You have the time for ACA / St Louis up to the abstract deadline
(March 7, 1997:-).
If you have other 'well defined' unknowns to add please contact me.
Armel