new
empty 1
head
  next
  next0
exit
size 0
push_front 5.5
front 5.5
back 5.5
push_back 7.5
front 5.5
back 7.5
count 7.5 1
count 6 0
pop_back 7.5
count 7.5 0
head
  next
  retrieve 5.5
  next
  next0
exit
erase 5.5 1
empty 1
size 0
delete
summary