anchor.diff:  		it: list_iterator;
   		tmp: longInt;
   	begin
  -		it := m_end;
  +		it := get_end();
   		it.prev();
   		tmp := it.get_data();
   		erase(it);
  
positive.code: 		new(link, create(data));
  		if empty() then
  		begin
  			writeln('empty');
  			m_begin := list_iterator.create(link);
  			m_begin.getLink()^.setNext(m_end.getLink());
  			m_end.getLink()^.setPrev(m_begin.getLink());
  
negative.code: 	end;
  
  	function list.get_begin(): list_iterator;
  	var
  		it: list_iterator;
  	begin
  		it := list_iterator.create(m_begin.m_link);
  		get_begin := it;
  	end;
  
  	function list.get_end(): list_iterator;
  	var
  		it: list_iterator;
  	begin
  		it := list_iterator.create(m_end.m_link);
  		get_end := it;
  	end;
  
  	procedure list.push_back(data: longInt);
  	begin
  		insert(get_end(), data);
  	end;
  
  	function list.pop_back(): longInt;
  