anchor.diff:  
   		public
   			constructor create();
  +			destructor  destroy();
   
   			function start(): Iterator;
   			function finish(): Iterator;
  
positive.code: 	begin
  		if p = tail then
  			exit();
  		if p = head then
  		begin
  			prevIt := head;
  			head := head.next();
  
negative.code: 
  	constructor List.create();
  	begin
  		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);
  