var last = 0;

function hide(x) 
{
    var el = document.getElementById(x);
    if (!el) return;
    
    el.style.visibility = "hidden"; 
}

function show(x)
{
    var el = document.getElementById(x);
    if (!el) return;
    
    if (last) last.style.visibility = "hidden";
    el.style.visibility = "visible";
    last = el;
}