Date: 17 JUL 1980 1635-EDT
From: ALAN at MIT-MC (Alan Bawden)
Subject: the cross design
To: RP at MIT-MC
CC: CUBE-HACKERS at MIT-MC

Yes, the cross design is possible.  I will let BSG try and describe it
if people want.  It is fairly straightfoward to tell if a position is
reachable.  I am thinking of onlining the proof that there are 12
equivalence classes of cubes (I think I have a fairly simplified
version), and if I do it should contain an algorithm to tell if a
position is reachable.