//
// plop
//
function plop(obj)
{
  if(document.getElementById(obj+'bis').style.display == "none")
  {
    document.getElementById(obj+'bis').style.display = "";
	document.getElementById(obj+'th').src = "design/minus.gif";
  } else {
    document.getElementById(obj+'bis').style.display = "none";
	document.getElementById(obj+'th').src = "design/plus.gif";
  }
}