function wechsel(box)
{ 

if(document.getElementById("b"+box).style.visibility == "hidden")
{
box.checked = false;
document.getElementById("b"+box).style.visibility = "visible";
document.getElementById("b"+box).style.display = "block";
}
else
{
box.checked = true;
document.getElementById("b"+box).style.visibility = "hidden";
document.getElementById("b"+box).style.display = "none";
}
}