var currenttab;

function showtab(tab){
    if(currenttab)closetab(currenttab)
    currenttab = tab;
    document.getElementById("tab" + currenttab).style.display = "block";
    document.getElementById("link" + currenttab).style.display = "none";
}
function closetab(tab){
    document.getElementById("tab" + tab).style.display = "none";
    document.getElementById("link" + tab).style.display = "block";
}