new
push_front 3
push_front 7
assign
  pop_front 7
  size 1
  delete
exit
front 7
back 3
count 3 1
count 5 0
count 7 1
head
  retrieve 7
  next
  retrieve 3
  next0
exit
pop_front 7
head
  retrieve 3
  next0
exit
front 3
back 3
pop_front 3
size 0
empty 1
delete
summary
exit