function show_nav(myID) {
    var myItem = document.getElementById(myID);
    myItem.style.display = "block";
}
function hide_nav(myID) {
    var myItem = document.getElementById(myID);
    myItem.style.display = "none";
}

function show_nav_un1() {
    var myItem = document.getElementById('un1');
    myItem.style.display = "block";
}
function hide_nav_un1() {
    var myItem = document.getElementById('un1');
    myItem.style.display = "none";
}
function show_nav_un2() {
    var myItem = document.getElementById('un2');
    myItem.style.display = "block";
}
function hide_nav_un2() {
    var myItem = document.getElementById('un2');
    myItem.style.display = "none";
}
function show_nav_un3() {
    var myItem = document.getElementById('un3');
    myItem.style.display = "block";
}
function hide_nav_un3() {
    var myItem = document.getElementById('un3');
    myItem.style.display = "none";
}
function show_nav_un4() {
    var myItem = document.getElementById('un4');
    myItem.style.display = "block";
}
function hide_nav_un4() {
    var myItem = document.getElementById('un4');
    myItem.style.display = "none";
}