new
empty 1
begin
  next0
exit
size 0
push_front 5
front 5
back 5
push_back 7
front 5
back 7
count 7 1
count 6 0
pop_back
count 7 0
begin
  value 5
  next
  next0
exit
erase 5 1
empty 1
size 0
delete
summary