anchor.diff:  
   	constructor List.create();
   	begin
  -		tail := Iterator.create(nil);
  +		tail := Iterator.create(0);
   		head := tail;
  +	end;
  +
  +	destructor List.destroy();
  +	begin
  +		writeln('Delete list');
  +		while not empty() do
  +			erase(start());
  +		tail.destroy();
   	end;
   
   	procedure List.push_back(element: longInt);
  
positive.code: 		prevIt, currentIt: Iterator;
  	begin
  		currentIt := Iterator.create(element);
  		if head = tail then
  		begin
  			head := currentIt;
  			head.setNext(tail);
  
negative.code: 
  		public
  			constructor create();
  			destructor  destroy();
  
  			function start(): Iterator;
  			function finish(): Iterator;
  