anchor.diff:  			
   			procedure next();
   			procedure prev();
  -				
  +			
   			procedure set_data(data: longInt);
   			function get_data(): longInt;
   			
  
positive.code: 
  	constructor list_iterator.create(l: list_link_pointer);
  	begin
  		m_link := l
  	end;
  
  	procedure list_iterator.next();
  
negative.code: 			nextLink := p.getLink();
  			link^.setNext(nextLink);
  			nextLink^.setPrev(link);
  			m_begin.destroy();
  			m_begin := list_iterator.create(link);
  		end
  		else
  