var OP_LAYER_OBJ = null;
  function showHideLayers(id) {
    var objLayer = document.getElementById(id);
    if (OP_LAYER_OBJ != null) {
      OP_LAYER_OBJ.style.display = "none";
    }
    try {
      objLayer.style.display = "";
    } catch(e) {
      objLayer = null;
    }
    OP_LAYER_OBJ = objLayer;
  }