function hekjeSluiten(toets)
{
var keynum;
if(window.event) // IE
  {
  keynum = toets.keyCode;
  }
else if(toets.which) // Netscape/Firefox/Opera
  {
  keynum = toets.which;
  }
if (keynum == 51)
	{
	var ditscherm = window.self;
	ditscherm.close()
	}

}