00100	Ian Braid  "Designing with Volumes" University of Cambridge
00200		Cantab Press, Cambridge,England
00300	DEFINE box1 BOX
00400	
00500	To maintain a point fixed, transform point to origin, make transformation,
00600	then transform back.
00700	
00800	COMBINE obj1 obj2;  merges coplanar faces
00900	INTERSECT obj1 obj2 allows negative volumes