function switch_layer1(id)
{
    var maincell = document.getElementById("main1");
    var layerlist = maincell.getElementsByTagName("div");

    var i = 0;
    for (i = 0; i < layerlist.length; i++)
    {
        layerlist[i].className = "clayer_hidden";
    }

    document.getElementById(id).className = "clayer_shown";

}


function switch_layer2(id)
{
    var maincell = document.getElementById("main2");
    var layerlist = maincell.getElementsByTagName("div");

    var i = 0;
    for (i = 0; i < layerlist.length; i++)
    {
        layerlist[i].className = "clayer_hidden";
    }

    document.getElementById(id).className = "clayer_shown";


}
function switch_layer3(id)
{
    var maincell = document.getElementById("main3");
    var layerlist = maincell.getElementsByTagName("div");

    var i = 0;
    for (i = 0; i < layerlist.length; i++)
    {
        layerlist[i].className = "clayer_hidden";
    }

    document.getElementById(id).className = "clayer_shown";

}