anchor.diff:  			nextLink := p.getLink();
   			link^.setNext(nextLink);
   			nextLink^.setPrev(link);
  +			m_begin.destroy();
   			m_begin := list_iterator.create(link);
   		end
   		else
  
positive.code: 		new(link, create(data));
  		if empty() then
  		begin
  			m_begin := list_iterator.create(link);
  			m_begin.getLink()^.setNext(m_end.getLink());
  			m_end.getLink()^.setPrev(m_begin.getLink());
  
negative.code: 		list = class
  		public
  			constructor create();
  			destructor destroy(); override;
  			
  			function get_begin(): list_iterator;
  			function get_end(): list_iterator;
  