anchor.diff:  			nextIt, prevIt: Iterator;
   
   		public
  -			constructor create(it: pint);
  +			constructor create(element: longInt);
  +			destructor  destroy();
   
   			function next(): Iterator;
   			function prev(): Iterator;
  
positive.code: 		insert(finish(), element);
  	end;
  
  	procedure List.insert(p: Iterator; element: longInt);
  	var
  		pelement: pint;
  		prevIt, currentIt: Iterator;
  	begin
  		if head = tail then
  		begin
  			new(pelement);
  			pelement^ := element;
  			head := Iterator.create(pelement);
  			head.setNext(tail);
  			tail.setPrev(head);
  			exit();
  		end;
  		if p = head then
  		begin
  			new(pelement);
  			pelement^ := element;
  			head := Iterator.create(pelement);
  			head.setNext(p);
  			p.setPrev(head);
  		end
  		else
  		begin
  			prevIt := p.prev();
  			new(pelement);
  			pelement^ := element;
  			currentIt := Iterator.create(pelement);
  			prevIt.setNext(currentIt);
  			currentIt.setNext(p);
  			currentIt.setPrev(prevIt);
  
negative.code: 
  		public
  			constructor create();
  
  			function start(): Iterator;
  			function finish(): Iterator;
  
  