a b c d   
d c b a   
b d b d b  b d c a c  c c d d d  a a b a c  a a b b d  
c d c b a  c a d d b  c b a c b  c c b c a  c b c a d  
a d a d a  c a a c c  d a d a c  b a d a c  b c c b c  
c b c a d  b a d a d  a c b a b  c d a d a  c b a b c  
bccaa cbcdb accba bdbac cdbdb bcdbd dbaaa bdbad ccadc caddd 
bbdda bbccb dadac badbd daadb cbbcc adbcc acdda babbb dbbda