function display(layerNumber)
{
   hideLayers();
   layerName = "layer"+layerNumber;
   document.getElementById(layerName).style.visibility="visible";
   currentLayer = layerNumber;
}

function ShowNextLayer()
{
   if(currentLayer == 3)
      {
         document.form.submit;
      }
   if (currentLayer < 3)
      {
         currentLayer++;
         hideLayers();
         layerName = "layer"+currentLayer;
         document.getElementById(layerName).style.visibility="visible";
      }
}

function ShowPreviousLayer()
{
   if (currentLayer > 1)
      {
         currentLayer--;
         hideLayers();
         layerName = "layer"+currentLayer;
         document.getElementById(layerName).style.visibility="visible";
      }
}

function hideLayers()
{
   var layerName = '';

   for (i=1;i<=3;i++)
      {
         layerName = 'layer' + i;
         document.getElementById(layerName).style.visibility="hidden";
      }
}