From: r_delaney2001@yahoo.com   
      
   I picked up book of optical illusions recently.  Mostly   
   color plates, very clever.   
      
   They fall into three classes, roughly:   
   i)  "hidden picture": the demon becomes an angel,   
    when the picture is rotated   
   ii)  impossible structures, a la M.C Escher   
   iii)  jumping structures:  a 3-D object jumps between   
    two orientations, before your very eyes!   
      
   I wonder, could one write a program, to analyze and   
   recognize cases (ii) and (iii)?  Can we describe them   
   mathematically?  This is really a computer vision problem,   
   but still of interest to opticians.   
      
   --   
   Rich   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)