CDL macros
d c b a 
advancing head pointer
c b a d 
c b a d c b a d c b 
c d a b c d a b c d 
deleting b
c a d 
deleting (a)
c d 
deleting (c)
d 
deleting (d)

DL macros
c b a d 
deleting c
b a d 
deleting a
b d 
deleting b
d 
deleting d

LL macros
c b a d 
deleting c
b a d 
deleting a
b d 
deleting b
d 
deleting d