function events_clicked(){
    var prev = document.getElementById('events').style.display;
    document.getElementById('events').style.display = prev=='none'?'block':'none';
    document.getElementById('memory').style.display = prev;
}
function memory_clicked(){
    var prev = document.getElementById('memory').style.display;
    document.getElementById('memory').style.display = prev=='none'?'block':'none';
    document.getElementById('events').style.display = prev;
}