function close1() {
 this.document.getElementById("fenster").style.visibility = "hidden";
}

function open1() {
 this.document.getElementById("fenster").style.visibility = "visible";
}


function close2() {
 this.document.getElementById("fenster2").style.visibility = "hidden";
}

function open2() {
 this.document.getElementById("fenster2").style.visibility = "visible";
}


function close3() {
 this.document.getElementById("fenster3").style.visibility = "hidden";
}

function open3() {
 this.document.getElementById("fenster3").style.visibility = "visible";
}